Pins are as predictable as real estate - and as useful as income property. Whether you keep the nice one or two (or more) for yourself, or rent (route) them out you will have to take into consideration much of the same upkeep and upgrade decisions (relatively speaking) with the same certainty of appreciation potential.
Buy it because you like it (in either case, for either purpose). In the case of a keeper, sometime down the line the market might present a buyer that appreciates the care one puts into something they like and will pay the premium. But I'm not sure you want to bet your retirement on it.
As for a collector pin, don't build it because you think it'll be an investment. I'm not sure I'd put a whole lot of capital (at least all at once) into a pin upgrades as an investment. If you have a pin you like, and you maintain it so it plays as it should, I can't think of a day that someone wouldn't be willing to pay at least what was paid for it. Unfortunately, like real estate, while upgrades will improve resale, the full amount of the upgrades are rarely realized at sale.