I thnk by addding Gewn is a great idea only because Pete needs a change from the MJ scene. Pete an MJ never really found that happy factor and there is always the second or love triangle that gose on. Right after 2, Sam went into production for stroy and all for 3. Do you remember the rumors that the Black Cat was gonna be in 3? I sure do, Sam wanted to spice things up in the MJ world so we could see that confortation in himslef as to what he wants. Each movie has it's theme. The last movie was about finding himslef as Spiderman, why does he need to be spiderman. This is about the darkerside of that. He now has everything he wanted. The girl of his dreams, the responsablity of spirderman dose not weigh in on him. Everything is perfect, but all good things come to and end and nothing good last forever.
Yea gwen will probably die in the movie which in turns fules Pete's hate, ( black suit made him go crazy, kill his best friend, lose the suit ). Sandman is the arch villian. He will be used to set up the symbiote story. Kinda how in the cartoon version of Spiderman ( the 90's ) We saw Teh Rhino and Shocker. But I hardly dobut they will use anything space in spiderman 3. IT just does not hold well in the movie relm.
I think just maybe that...................The suit or symbiote was made to help cure cancer Harry help funded this research. For all reasons or what not Sandman needs a reason to get this cure ( he is to have a wife and or child in the movie) Spiderman comes to stop him, Bang he gets the suit. Then the all out Harry vs. Pete begins. Meanwhile, Pete is changing he is drifting away from MJ Gwen messe with that. Eddie was fired Because Pete is doing such a great Job, Spidy screws over Eddie. All of the hate and betral and lies is due to the suit. Which I think he will sport in most of the movie. By the end we see the clasic bell tower scene adn A small glips of Venom of or sound maybe a shadow.
Thats how I would do it, and being that Sam has done a good job with 1 and 2 I think this one will hold fine, Also Chris Nolan ( Batman Begins ) shows that puttin to villians in a movie can work well and still have a comic esque feel to it.