Agree, but at the same time, how many good 4th, 5th, or 6th movies have you seen. Usually the 3rd movie of series sucks too, unless, in many cases, the series is pre-planned out as a trilogy. One big reason I think that TDKR won't be a bad 3rd movie, it's been planned as a trilogy, to have a beginning, middle, and end. If they feel that they can pull off a fourth or more movies, then by all means, do it. I almost feel like you could combine the alien costume story with the Clone Saga for a back to back 4th and 5th movies. And then have a big finale movie in the 6th.
I guess what I'm saying is do classic spidey stories for 1-3, then start the clone saga and introduce the alien costume in 4, continue clone saga and introduce venom in 5, and then have maybe Carnage and someone else in 6 to wrap up the whole series.