1) I think Mitsubishi's are about as good as any other, simply less demand equates to lower price. Chrysler did ( or maybe still does ) have a piece of them, and with the global economy being what it is, I"m sure Mitsubishi parts are used in many other vehicles, as well as they use pieces from other manufacturers.
2) As far a lease return vehicles go, I think it largely depends on the vehicle. If it was originally a low cost vehicle, then I think it might be a safe assumption that someone who could not get credit to buy it went the lease direction, and quite possible did not maintain it properly, and/or beat the stew out of it...like you said, treated it like a rental
If it is a bit upper scale, then I think that there is a better chance that it was leased for business reasons ( IRS), and then simply returned, and another leased vehicle obtained. Bottom line, if I were to purchase a lease-return, I'd only do it if service records were available, and if it came back clear ( no wrecks ) car-fax. Even then, if it was an upper class vehicle, I'd have an idependant mechanic check it out.
Mark