I pretty much agree with you, dude. Venom as a character is really overrated, and he really only works as a Spider-Man villain. 
I love Venom, but he was ruined in Spider-Man 3. He in no way deserves a spin-off movie, especially if it has nothing to do with the Spider-Man franchise. 
Now, a lot of people might disagree with me, but I think that if you wanna see Venom again you need to bring him back for Spider-Man 5 or 6, after enough time has passed and people forgot about him. I think he could (kind of) easily be brought back, even with Topher Grace, and be given a great villain arc in the films, culminating in Venom killing Gwen Stacy, by then Peter's girlfriend. There are a lot of great things about Venom and, more importantly, Eddie Brock that weren't addressed in Spidey 3 that would be really cool to see in like part 5. 
But bottom line, don't do a spin-off. If you wanna see him again, bring him back for Spider-Man 5. (And make him a total evil bad-ass, too.)