3) Family/time. You go crazy with upgrades and realize, crap, I don't have time to run them. I'm in this boat...but I'm not getting rid of mine. When I do have a chance to run them, it's a freakin blast. Plus, mine are all paid off.
Yeah, this is my position. My cars are paid off, I just lose so much time to family and career that I've very little left for my beloved R/C. Which figures...but like you, I'm never getting rid of my cars. I made that mistake before, and regretted it ever since (I had a Tamiya TGR w/the fabulous FS-15RB engine and an M8 transmitter, like an idiot I sold it), so never again.
There are always those who will try to get what they put into it, because they do what I normally do...I find something on eSlay that seems like a good deal, but just needs some work, next thing you know you've replaced nearly the entire machine and are out almost as much money than if you'd just bought a new one. 'Course, I guess I don't honestly mind it, so much...I'm not into spending money on stuff I shouldn't have to, but I do like the quest of finding parts and putting stuff together. Even so...if you're not frugal, you'll find you could have bought the high-end version for what you spent
anyway, and then perhaps in a panic to get that money back they try to sell it for what they've got into it.
The only item you can do that with is homes and businesses. Everything else has a static value and you won't be able to squeeze $3k out of car that cost $900 new. Sure, if you upgrade it, the whole car is alloy and the best-of-the-best, then maybe somebody would be willing to buy it for an inflated price. Though I doubt that very much.
Word to those looking into getting R/C of just about any scale: 1). you get what you pay for (unless it's eSlay), and 2). if you don't like to tinker, fiddle, or take stuff apart and put it back together, best you stay out and buy something you will like with that money. R/C takes a particular kind of individual, and especially if you buy something off eSlay with the intent on renovating or restoring it. Get ready to spend money, time, blood, sweat, and even tears to get it right. If that's not what you're looking for out of this hobby, you might want to rethink spending the money.