You are contradicting your thematic statement, You are implying new cameras, DSLR vs Mirrorless. Both, as new cameras, have the same warranty, the same long-term parts supply and the same cost. Say Nikon D850 and Nikon Z7 or whichever Z you want to compare. The choice between the two comes down to looking at the world through a prism and mirror or a video screen. There are personal preferences for either. Then there is the issue of existing lens ownership, only the G seies andf later lenses work with AF with the FTZ, and adapters are a pain, so there's that.
Now let us look at the used market, there the differences continue, a D800 vs a Z6, now we are getting closer, still even more so rthe costs and lens selection are an even greater determining preference. It's the lenses mostly, and 36 mpix.
Kinda sounds like the old audio arguments when CD's came out, everyone starting dumping their records, that's when I built my collection and had all the high-end TT's to appreciate them on, but...Digital turned me around, sold my records (most of them) kept one simple to use state of the art B&O TT and carried on building a high-end CD collection now super cheap. But I digress a bit to prove a point.
Sysyems come and go in popularity, Mirrorless is the future, not all of us like it or can afford it
I always debate between using my Nikon D700's, D300s or my brace of Olympus OMD-e5's. I tire of the confusing little buttons on the OLY's but like the size for travel. I get great pics from both, horses for courses I guess

Pro level Nikon’s are the toughest cameras on the market, they are designed to get the image first and foremost. Two quickies: my FE-2 (1982) fell down some steps in an old mosque in Pakistan, never missed a beat.
Two weeks ago I slipped and fell on concrete , my D700 free fell a good 3’ onto asphalt, no problem!

Ironically the 28-300 out performs the 70-300’s made by both companies, esp between 28-70 😎

The made in China lenses are not as good. The afs 24-120 f3.5-5.6 be was first made in Japan, good not great lens, the later ones were made in Thailand and sucked. All the Thailand and China Nikon lenses suffer from long term quality control and dependability issues. Never had a problem with an ais or d lens. Lots of problems with G lenses: 25-120 f4 failed zoom helical, 55-300 D focusing helical. Never had a problem with a made in Japan Nikon item.

I'm here still, I cannot respond via my phone as the format of UH prohibits it due to some weird loading thing (page goes white and I can read responses but cannot respond).

Well I finally figured out how to lock my focal point, i do a lot of focus and recompose, this has brought me closer to a more "amorous" relationship with the M1, never had a problem with my M5.

Anyway, GAS is a powerful force with me, I do have a minor investment in the more mature versions of the Oly system (E-M1, E-M5 and E-p3) and have been contemplating the disposal of my 80-400 D and D300, and other equally mediocre Nikon gear to fund the purchase of the 75-300 and 12-40 pro lenses (just have the various kit lenses now).
I know full well the pros and cons of my considered action but have difficulty, nostalgia? in disgorging my less than desirable middling Nikons. Biting the bullet so to speak may be the best choice.

The other alternative though, I was going to pursue a D3 to go with my 35-70 f2.8, Confused and unfocussed, hoping a change in approach whether re-dedicating myself to my dear Nikon, or to pursue a younger more attractive mistress, I used to "see" photographs everywhere I looked, that blessing seems to have passed due to age?, but that's how this mind torments it's possessor.

I should like to add, I am truly grateful for all the replies, hearing of other's experiences does greatly soothe the anxiety of decision.

I have always used Nikons and currently have a stable of D300s, a D7100 and a D700. I haven't a lot of money to throw at my hobby so I've always concentrated on value. I have a few "better lenses" but have recently been using my Olympus E-M1 mki and e-M5 mki. Despite some haptic issues due to learning curve I'm being tempted to go "all in" on the M43 system. Anybody else out there forsaken their long term affair for the experience of the m43 system, anything you miss? for me to really move up means selling or trading in what I have, there is trepidation afoot...

I have two solutions that are worth considering. The lenses in discussion currently are all very large and very expensive. however:
1. get the 70-300 VR, smaller lighter, gives you 450mm effective, and if you need more reach crop in a bit, the 5600 gives you plenty to do that with, or...

2. Micro Four Thirds is a viable alternative, the Olympus 75-300 is cheap and light and pretty darn good also, this gives you a small 150-600 equivalent zoom, much easier to handle, and the Olympus cameras are quite cropable.

Hope this helps...

Extreme wide angle on the B camera and the zoom on the A camera, Now will this be the end of it?

My field kit for landscapes consist of a D700 w/ Zeiss 25mm f2.8 and a Zeiss 28-85 mounted with an adapter on an old em-1 which provides a 56-170 “normal-tele” option.
I also carry a D7100 w/ 24-120 which has a polarizer on it, the 24-120 is a rare JAPAN! Made version of the second generation lens w/VR.

They don't "C***t" the workers, if they weren't there the workers wouldn't have jobs, every company doesn't c***t it's workers, sure they may be assholes, or insensitive, but the reality is those people chose to work there, it's better than their previous subsitance.

You’ll get more use out of the telephoto, super wides are nice to have but rarely necessary

I love my D2X, i use it with the old 25-50 and the 50-135 f3.5 for certain subjects and just to have fun

(Download)

you beat me to it!

I’ve owned and continue to own OMDem-5,m-1,ep-5. Great image quality, lotsa lenses. Not impressed with dependability, battery life and menus. 2/3 cameras have needed shutter or sensor replacements out of warranty. Battery life sucks, my Nikons always work, not so much the Olympus. But for travel they’re great

The way the D700 plays with manual focus lenses is lovely, the D700 is a classic, a well regarded well designed terrific and affordable FF camera, I love mine, more than my D7100.