So I've recently been running into these promo and review copies of games. Loco Roco 2 for the PSP and a lot of 360 titles. The way I understand this, at the moment nobody is interested in them and the price is roughly the same as a used copy, if not a tad less.
Do they get more expensive faster than normal games or the other way around? Are these things worth anything? Should I always prefer a normal copy or get these promo and review copies whenever I see one?

Thanks, guys. I know you guys know this shit.

Happy new years!