"Wasting" Gwen didn't really bother me at all. The average non-fan doesn't care or know who she is and Raimi needed to have someone in the movie for Peter to date to make MJ jealous. So why NOT Gwen, as a little "in joke" for the rest of us? To me, it was no worse than the way that Singer used Rogue in what should have been the Kitty Pryde role in X1 and X2.
Hell, if any comic book movie "wasted" a classic supporting character, it was the first Burton "Batman," which had Harvey Dent being played by the great Billy Dee Williams and then didn't use him as Two Face in "Batman 2."
After all, at this point, between the "Ultimate" book doing the backward continuity already (and having someone other than the Goblin kill Gwen) and the complete fan wank ass (and vaginal) raping that JMS gave the character in Amazing, its not like Gwen remains a "sacrosanct" character even in the books. So why bitch?
If I have a minor quibble with it, its that you already had the hot, hot, HOT Elizabeth Banks right there as Betty Brant, who is also one of the Peter's exes in the book. Instead of bringing in Gwen, they should have just expanded the role of Betty and used her to make MJ jealous.