Jeffrey, if you wnat a test of patience, try converting and old Varney, or Athearn Hi-F to DCC. I've fried more decoders on those engines than any other. Pretty much amp hogs.
I've been working on restoring a few engines lately. Old Varney steamers mostly. Parts are plaentiful, not too expensive at all through Yardbirds. When finished, I'll have 4 updated 60 year old engines.
And my collection of old Athearn Hi-F's is rivaled by few. I bought a lifetime supply of rubber bands at Dollar Tree. Cost? $1.00.
I have about a dozen P2K engines that have had their gears changed due to breaking. And my Spectrums have had to have their railings replaced by metal replacements. About the ONLY newer engines I haven't had to repair are my Katos, and Atlas/Roco power. Those are the diesels.
On the steam front, the best newer engines , IMO, are the Rivarossi Red Box engines. And those aren't made any more, but are available on eBay and from the back rooms of LHS's. Real horses when it comes to power, and very sturdy, though some of the finer details need care when handling. Spectrum, BLI, and the rest leave a bit to be desired. They sure look nice but mechanically are turds.
Some of these "newbs" have nothing to compare the new stuff. They think it is all top shelf. NOT!!!! They wouldn't think of buying a 40 year old engine, or even a 20-year old one, fixing it up, detailing it, and placing it on their layout. Maybe it's the thrill of owning the "latest and greatest". A bit of "look what I got" and a bragging rights I guess. I'd place ANY piece I have, ANY, against ANY of the new stuff. I know of no "new" engine that can pull 329 coal cars by themselves without MU'ing. I have a an"old" engine that will do that and more, we ran out of coal cars for that demonstration. Bragging a bit here, but ............
Is the "new " stuff better? Ask me in 40 years....
Bob
It's interesting how this "the old stuff is better than the new stuff" theme creeps into so many threads. Is it really though? To offer some different opinions:
I have never had cracked gears on any of my P2K locos. That was a problem early on because they machined the holes in the gears too small. It has long since been resolved. Lifelike and Walthers gave away God only knows how many free wheelsets, probably enough to re-wheel more locos than were made, to fix the problem. It got so ridiculous that they finally started charging for them. If you buy "old new stock" out of swap meets, or on e-Bay, it is still possible to run across them I guess, but I never have. Just lucky I suppose. I just popped the tape on an old P2K E-6 this morning to install a decoder. It's an old first run I bought out of an estate. Has a dummy plug in it, but the old Athearn style motor, and essentially an Athearn BB style drive train. I trash the P2K boards anyway and just hardwire in decoders
I don't miss the old too wide hoods on the BB GP-7/9's and SD-9's, and the too large BB F-7 windows, the current hog motors, the iron wheels, the cast on grabs, and all that. Not at all! And I don't really miss buying a $40.00 BB, then adding $75.00 worth of detail parts to get it close. I don't miss the days of one model lettered for every road under the sun. I can still add detail parts to the newer stuff if I want an exact match for a prototype, so the art isn't dead or dying, you just don't have as far to go to finish. I have sold most of my old BB stuff as better models became available, but still have a bunch of BB switchers, and a lone GP-35, and I still superdetail, but I like having a better starting point and less gross errors to correct.
Will the new stuff still run in 60 years? Well since at that time I'll be 115 years old, I hope I'm around to find out

, but actually I think it will. With normal maintenance, no reason it shouldn't. The old stuff wears out too. Talk to CJ and ask him how many old Pittman motors he's rebuilt, or even better, go look at that layout in Chattanooga that runs constantly and check out their exhibits of worn out equipment.
Red box Rivarossis? Only ever bought one. Thought it was the grandest thing at the time but...that crappy old AHM three pole motor they had in it wasn't worth the powder to blow it to Hades, and the running gear quality was very poor. I still have it, but it's a roundhouse queen. Sentimental value only. Now there was a mechanical turd!
The newer steam from BLI and spectrum looks good and runs well in my and our clubs experience. Very little trouble from it. The move to diecast boilers is doing wonders for pulling power as well. Our club got one of the new Paragon Y-6b's, and it runs great, and will pull the plaster off the wall. You can also pick it up without breaking something. Plenty of older generation BLI stuff is around as well. We use them regularly in operating sessions. They run like clocks. I'll give you this though...it takes more skill to work on them than older steam and older brass, and there isn't much of anything in the way of aftermarket parts. OTOH, they haven't needed much of anything.
I think that it's less a matter of quality than a matter of doing what you enjoy. If you like the old stuff better, more power to ya! Likewise if you like the new stuff. It's about doing what floats your boat.