I know that's just my personal experience and Nokia are probably a lot more reliable now, but I'm still struggling to bring myself to buy another Nokia based on past experience.
Sometimes you get lucky - sometimes not.
Take me, for example. 6230 was fine and dandy, if getting a bit old by 2009. The N95 crashed all the time. Switched to Samsung in 2010, but now my Galaxy S acts like the N95. Sometimes you get lucky, sometimse you don't. Other times, it's just the software and hardware can't catch up to the modern age.
Anyway, when you buy a phone, you should consider the phone on its own merits
without bothering about the future - you should buy based on current needs and not worry too much about software updates. Even if a phone can't be updated much, if the phone's functional, there's no real reason to. Do also give weight to the phone manufacturer and carrier, though the manufacturer ideally shouldn't be much of a factor.