Spiderman 3 will make more then the second movie , but IMO less then the first movie..
The first movie had a combination of factors that ultimately proved to work really well for the movie's BO.
It was , if i'm not mistaken, the first movie that brought back the audience to the cinemas after the 9/11 attacks.
When it was announced that Sam Raimi was going to direct it , many people loved the idea simply because Raimi delivered great movie such as the Evil Dead movie.
Casting Tobey meant that they were actually using someone who could act.
And if i have compare SR with this , it shows just why CGI was made to make the transition from comics to movies.
Spiderman had a superhero villain. Everything from the glider to the sadistic laughs ( c'mon DAFOE PLAYED the role incredibly well). It all just fit right.
With Spidey 2 , depsite it being touted as the better movie , personally i don't that is true. While CGI is leaps and bounds better then the first movie in terms of realism and fluidity , i think the 1) pacing was bad ( the first 1/3'rd was good , the second was a snoozefest and last third was all out action) , 2) Molina while being a great actor really missed the makro of being menacing. Dafoe made lines that sounds silly on page , sound great "We'll meet again SPIDERMAN !!!!" whereas Molina didn't IMO ( Butterfingers , The power of the sun in my hands).
And 3) the love story. It was just something that look forced and a really in you're face type of lovestory. It just didn't feel natural and realistic.
And it showed at the BO. While still performing as a massive blockbuster , Spiderman 2 made less domestic and internationally.
But with Spiderman 3 , i think they'll have alot of things settled.
The pacing would seem to be improved. With essentially 2 villains dominating the movie ( Venom will most likely be shown at the end ) i don't think there will be whiny love stories. Spidey will be needed all over the place so there will be a fair bit of action.
I'll reserve my judgement of the villainous performance of THC until after i've seen the movie. Visually at least , the fights between SPiderman and Sandman will be awesome. No doubt. I had my fears when i thougt that sandeffects would look like the mummy but with the teaser and the comic-con footage , i think they got the efefcts working right.
James Franco shows that he can act and i do think he'll make a great goblin. And if hopefully they can get more scenes with him and Dafie pumping him up , it would be even better .
Venom is of course the fan favorite that many would want to see. But IMO it's only reserved til last , so we really should have to do with Eric Foreman

acting all humany and stuff.
Which leads me to the next point.
Spiderman/Peter parker and the symbiote. I'm really interested in seeing these aspects explored. And with the rumors of THC being in someway connected to Ben's death , it would definately make for a interestig way of portraying you're heroes as flawed and almost egomaniacal.
Spidey 3 looks like an improvement of Spidey 2 , but given the subsequent release of Shrek 3 and the major movie to beat , POTC3 : AWE , i don't see this movie making more then the first one domestically. It will surpass the second one .