Look at this forum: It's kinda scary: What good is it to upgrade? (brand new phone)

[gguruusa]

Wow. crazy stuff people think.

Upgrading
1) will sometimes make your phone a little faster/more responsive. But only a little.
2) does remove crap software that no one uses
3) will let you utilitize otherwise unused memory, depending on your device (not for titan)
4) will build software programs and tweaks and themes right in, saving you the trouble of doing it yourself. Only meaningful as compared to hard resets (locked up phone) and stock upgrades.
5) will generally fix minor software problems
6) will generally utiltize the latest software (like WM6.1)
7) will let you change splash screens

upgrades
1) will not get you better radio reception
2) will not get you a faster processor
3) will not get you more memory
4) will not get fantasically better battery life, unless your carrier screwed up the power saving option to begin with.
5) will not increase the resolution of your camera

kitchens
1) will let you fully customize your phone
2) are only marginally more difficult than flashing a pre-made rom
3) usually contain newer software than premade roms
4) are addictive. You will need therapy.

Edit: and if you don't have Sprint, but want GPS, you can get that only through an upgrade (because you'll need a new rom).