AFAIK, the evga step up prog on ONLY avilable in USA/Canada.
If u can get it, just do the maths. Evga cards are more expensive. Pretty sure u pay for postage when upgrading too. So u have that additional cost along with paying a little extra for TWO cards.
Many ppl like this prog, i wouldnt bother with it TBO.
Also... the limit IS 3 months, just make sure there will be a newer card available within that time. Id be sceptical that the 9800s will be out in 3 months.
As for th OP...
No the cards wont drop in price for some time
Yes u will see a decent boost if u got for a gts
Upgrade now (if u can/want) or wait till the new cards come out.