In my experience, I have rarely improved the sharpness of any photos using the "sharpen" tool in PSe.

You can use the tool to improve the quality of the noise, by making noise look more like "grain", and that is sometimes an improvement. (A certain amount of grain is pleasing to the eye, and makes the picture "look" more sharp than it really is.)

If you love taking pictures with all the filters turned off, you will occasionally get photos with way too much grain. In those cases, it is worth playing around with the "unsharp" and the various filters. The low-pass, for example, is really good at eliminating moiré patterns.

I tried a used D850 in the store a few weeks ago, and even though I have always used Sony, I almost bought the D850. It did everything well. The low light autofocus was surprisingly good, the color balance for skin tones was excellent, even the video autofocus was better than I had expected. The ability to lock on to a moving subject seemed (to me, in that limited test) to be as good as the Sony A7RIII.

Since you already have a D750 in the family, there is some value in having interchangeable lenses with no need for adapters. If you buy one high-end lens for the "family", then you don't have to feel guilty buying a lens that only works best for one of the two cameras.

The pixels in the cell phone are much smaller, but they work in the same way.

Generally speaking, if you have good light, and a slow moving subject, and no need to blur the background, a cell phone will take a picture that looks similar to, if not better, than a large-sensor camera. The cell phone has an advantage of a huge processor that can balance color to improve skin tones, enhance lighting, slim people down, or whatever. The dedicated camera will produce a more accurate picture, but people don't always want "accurate".

The big sensor will also start to pass the cell phones when it comes to low-light, fast-moving subjects, and blurring out the background. Cell phones can do a bit of this with computations, but it usually just looks like a half-finished mess.

An easy experiment: Take some pictures of buildings and sunsets outside in good light with a cell phone and a real camera. (Take the same subject from the same angle so you can compare the pictures.) Then go inside and take some pictures of dogs and kids in average indoor light.

For the outdoor pictures, it might be hard to tell the two cameras apart. For the indoor pictures, literally anyone will be able to tell the difference.

For people with chronic shoulder problems and back problems, I normally recommend cell phone cameras or small point-and-shoot alternatives.

The Sony RX100 is an excellent pocket-sized camera, but once you add the batteries, 8.5 oz.
The Canon G7X Mii is actually heavier, at 10 oz.

The best way to save weight is to look at something like the Canon powershot ELPH 100, which is 5oz including the battery. This camera has a 1/2.3" BSI sensor, and a built-in f2.8-5.9 zoom lens. I think the range is 28m to 112 mm. Although it does not have a viewfinder, the image quality will be mostly better than any cell phone because of the zoom range.

If you are shooting in good light though, with a slow-moving subject, and no need to blur out the background, then a good cell phone will take as good a picture as any camera, and better than most.

I have been shooting Sony for a while, but I usually don't recommend that people switch to Sony unless there is something they really dislike about their current camera.

The Nikon D3500 right now is about $500 with the two kit lenses, and the D5600 is about $800 with the same lenses. If you still have the two lenses, then you can get the D5600 for less than $500 if you look around, or the D5500 (if you can find it at all) cheap.

The D5600 and D5500 both have a nice touchscreen, and nice autofocus. I think Nikon added their snapbridge software, or something like that to the D5600, but even loyal Nikon users have told me that it is not a feature they would pay a lot extra for.

You can pay a lot more for a camera, but I wouldn't do it unless you have a specific need.

Between iPhone and Samsung, the camera capabilities are pretty similar. Nikonbug is correct that the software in the Google Pixel 3 is a little ahead of the other two big players right now, but it is a pretty good bet that the other big players will catch up in due time.

The capabilities of software enhancement have not even really been tested yet. There are software programs that run on your phone that can automatically fix your make-up, smooth your wrinkles, whiten your teeth, and remove those dark circles under your eyes. This lets the photographer concentrate on things like lighting.

If you are talking about Sony, it seems like the treat grey market cameras pretty much like "out-of-warranty" cameras. They will replace any parts that they can identify as broken, and the parts and labor charges don't seem to go up or down based on where you purchased the camera.

Sony has a reputation for not fixing cameras under warranty unless it was a manufacturing defect, so in some cases, the grey market cameras will give you identical service to the U.S. version.

One thing to worry about is that the grey market lenses are sometimes poor copies. I am not sure why this is, but I have heard several users complain that their 70-200 GM was "never quite right". Unfortunately, just having a bad copy is not a problem that Sony (or anyone else) will have much luck fixing.

I am not sure if it is covered in the manual, but you can turn face detection / eye detection on in the menu under Matrix Metering. Then if you put the camera in Auto Area AF, then face detection will work on AF-A, AF-S and AF-C.

I think it will also work in Group AF, as long as you are using AF-S.

Unless you need to freeze motion, or blur the background, or use low light, cell phones are fine.

Have fun on your holiday. Be sure to share some pictures with us when you return.

Wait, "Release without lens" resets after each picture? Or do you mean it resets when you turn the camera off and back on?

The feature was (kind of) designed for people who put manual lenses (or telescopes or whatever) on a camera. It is not supposed to reset until you turn the power off.

There is a 9" digital frame on sale at Amazon with 1067x800 resolution. That makes each image about 300K with minimal loss of quality.

That means an 8 Gig memory card will hold about 26,000 images.

Generally speaking, you want something that is weatherproof and a lens that goes out to at least 400mm. There are some excellent bridge cameras with 1" sensors that would do the job a lot better than people might think.

Although it does not have weather sealing, the camera that comes to mind is the Panasonic FZ1000 ii. Although the 16x lens is not as long as some of the "superzooms", some of the other zooms are so long that they are unusable.

The FZ 1000 ii also offers fast autofocus, an excellent macro mode, and a nice touch screen.

The Sony RX10 is almost as good, and offers better weather sealing, so those are the two I would look at first.

Any hike that long rules out a heavy tripod for me.

Since you have the 100-400, you aren't really giving up much to leave the 500mm at home.

In any case where you have good light, a slow-moving (and close) subject, and no need to blur the background, a cell phone will usually take better (or at least as good) pictures as a camera.

The big processors in the cell phones let them balance color better, and even sneak in a bit of HDR and edge detection.

On the other hand if you have poor light, a fast-moving subject, and you need to blur the background to highlight the subject matter, then a cell hone is going to give you a blurry mess.