You're right that there were no significant changes other than color choice and option availability. If you need GPS/Nav or DRL, avoid 2001. It seems likely that there were some software upgrades slipstreamed in 2002, so you may want to avoid 2001 for that reason also, but if you get a good price it may be worth it anyway.
Other than that, the new vs. used choice is very much dependent on your own situation and personality. Since you said in another post that you live in Mexico and may not be able to take advantage of the warranty, it seems like you'd be better off getting a used Prius to take advantage of the price break. Of course you also need to find one, which might be harder from Mexico.
Or you might want to wait 6 mo. to see what the 2004 model year brings. There's been some speculation that the Prius is due for an upgrade.