Whether it is worth it again depends on what you want from it. Will the top-of-the-line model be worth it over the base model? It depends entirely on what you want.

Using Canon full frame as an example, the top-of-the-line newest 1Dxwhatever is certainly better at many (most) things than the legacy 6D, but is it better for you? If you shoot sports or birds, then it probably is. You travel a lot, the 6D is likely better and on account of its light weight and excellent low-light capabilities is perhaps the best Canon DSLR of all for travel.

The Nikon Df is inferior in every specification, not to mention more expensive than the D810, but that doesn't stop many photographers from really enjoying its retro control layout and dials that can be preset with the camera shut off (I love mine and converted its focusing screen to an old-style split image). Even the newest D850 would still be "less fun" for me to use than the Df, despite its many advantages.

Leica is probably the best example of an over $5000 camera. Nobody really "needs" a Leica rangefinder, and while the image quality is outstanding, Leica's sensors are no better than Sony's or Canon's (no worse either in image quality, though deficient if comparing spec sheets). Leica's lenses are all outstanding, and outstandingly expensive, but as one example Canon's newish 35mm f/1.4 L II is every bit as good as Leica's 35mm f/1.4 Summilux at roughly 1/3 the price (and twice the weight and three times the bulk). Of course, Nikon, Sony, Canon and the like don't offer a proper rangefinder, and until they do photographers who like rangefinders will keep buying Leicas.

As I take on average less than 1,000 shots per year, I just can't justify spending $5,000 on a camera. Let's say I get about 15 years of use out of the camera... the estimated cost per image is still quite high when one does the math. And that's not including the cost of memory cards, external drives, and various photography accessories I may wish to purchase over that 15 year period. Then again, I'm just a hobbyist. The money I spend on camera equipment is not some kind of unavoidable business expense. I don't need to buy a $5,000 camera.