I'm 54 now and just a few years ago was having some physical issues that kept me from enjoying working on my car so I've let it sit. While those issues have past for the most part other things have kept me from getting back into working regularly on cars, I figure the Challey has waited this long another year or two will make little difference. Finances are not holding me back at this time, just so many other things that need attention.
Anyways it sounds like your contemplating jumping from a small money pit into a big money pit if selling what you have now only gets you a down payment. And consider this, anything that goes wrong with those newer models is probably something you would not be able to handle technically or physically so it would just mean more money to keep them going.
Simplifying by reducing your collection may very well be something to consider, you just have to determine what's important to you. Having just bought a new Challenger and while I do like the car it is no substitute for the real thing. I'm holding on to a '98 GT for my daily commute & I really enjoy driving it, was gonna sell it but for no more than it would bring and as solid a car it has been it's worth the little extra expense to keep miles and wear off the new car.
Have you looked into what's got ya down? A little lifestyle change has made a huge difference in how I feel. Lost a little weight by eating better, started getting some of the right kind of exercise and i feel better than I have in 10+yrs.