Skip upgrading is a frugal thing ... but be careful with it: Adobe has caught on to it and has changed their upgrade policies - - already, CS (ie, CS1) has been cut out of eligibility for later versions...
...and with them dropping in CS 5.5 in the sequence, I'd not be surprised if CS3 isn't eligible for CS 6.
If I were you, I'd take a look right now to see what the upgrade requirements are for CS5.5 ... if it is CS2, you'll probably be okay in taking the risk that 6 will allow upgrades from 3 ... but if 5.5 is already on 3, then I'd bet beers that your 3 is going to get dropped for 6 and CS4 will be the latest upgradable version.
Of course, being on a campus, you could just look at buying a new "Student version" as another less-than-full-cost option...
-hh