I'm in that situation. What is making the decision easier is the live.com promotion going on.If you want to order through a reputable webstore like J&R, you can get a 16gb for 289 and then get 7% off from the cash-back. So you would pay 289 and then in maybe 60 days you would get an addition $20 back. Hopefully it doesn't take the full 60 days but I don't think anyone has got it yet to know
Another route I'm seriously considering, ebay you can get 25% cashback right now. It has been up to 35%. So, I found a 32gb ipod touch 2nd gen for 370, found an ebay promo code as well for $25 off a $100 purchase. So you'd pay 345, then you also get the 25% off from using live.com for the search. The discount shows it applying towards the 370, so you will EVENTUALLY get $92 back. The total would be around $252 for a 32gb 2nd gen ipod touch. That is an amazing deal as long as there isn't too much hassle. I've never had a paypal account, so i don't know how that will be.
As far as your question about buying now or waiting, I would buy now. The past updates have all been around september after the educational promotion ends. If anything, I would bet on it only being a minor software update. IF that even happens.