Sell the games and system online. You're better off, unless the games are pretty much ones not many people would want. EB almost never gives you any decent trade-in deals.
Remember that they usually say "non-sport," too and you don't get full credit unless you have instructions and everything.
I sold my GC and some games, but only the "leftover" games were included. I had several more GC games--good titles too--that I sold already i.e. Viewtiful Joe for 20, Zelda Collection and Wind Waker for about 30 bucks each, Mario Sunshine for 15, Prime and the strat guide for 25....
That's over 100 bucks right there, not including the system. Of course, at this point those titles would probably be worth less, but still you're probably better off.
Check what half.com and Ebay have as the main prices for those games. If you'd only be able to sell 5 of the games for about 10 bucks each, do the trade in.
As for the PS2--I'd get one (as abominable as 90% of the game library is, it's still got probably the best actually number of good titles), but you may as well wait until the "PStwo" is out unless you really want the hard drive. It will save you the cost of the network adapter (if you're thinking of playing online) plus it's smaller and easier to find room for.
If the PStwo doesn't sound appealing, with it will come a cheaper price on the existing PS2 units. You don't need to get the PS2 right away.