Okay, first, I want to say that I have nothing against Topher Grace's performance in Spider-Man 3 in and of itself. I thought he was the most entertaining person to watch the whole movie. I also want to say I don't want Venom to return, simply because, in the context of the movies, his story arc is complete.
That said, it just hit me just how much they botched the possibility of a truly great, fleshed-out Spider-Man/Venom movie. Hell, they could have even reduced the entire symbiote saga into two movies: in one, Spidey gets the symbiote costume, goes through his whole revenge thing fighting another baddie, Eddie is introduced, Spidey realizes costume is bad, ditches it, Eddie gets the costume, end of the movie. Then, in the next movie, Venom tries to kill Spidey, they're enemies, they fight, they have their whole business, and then, at some point, Cletus Kassidy gets the symbiote spawn and becomes Carnage, wreaks murderous havoc, forcing Venom and Spider-Man to team-up, because Eddie isn't a totally immoral human being, they go up against Carnage, and somehow, Carnage and Venom both end up dying, but it doesn't feel like either of them are totally wasted.
There's really no way Venom could have NOT died, and there's really no way to get an entire film with Venom as a bad guy, because Venom is so singleminded in his pursuit of killing Spider-Man, that the ENTIRE MOVIE would consist of Venom trying to kill Spider-Man. That can work for one-fourth of a movie or so, but not an entire movie. Ditto goes for Carnage going around wreaking murderous mayhem, because it gets monotonous and eventually, way too many people have died to excuse Peter doing anything with his time OTHER than trying to stop Carnage. So, by stretching it out over two movies, it forces non-stop, monotonous action, whereas, over one movie, there would be lots of action, but it wouldn't get repetitive. Plus, the development of Eddie's character would feel much more satisfying and complete.
Now Carnage isn't even a possibility in Spider-Man, because Carnage is only effective as a plot device that forces Spider-Man and Venom to team up. Spider-Man alone against Carnage alone is stupid and serves no point and offers no potential for character development.
Either way, reducing Venom to a single-scene in a single movie was inexcusable, and it would have been entirely possible for them to contain Venom and Carnage in one movie effectively.
Damn Sony.