Lizard is AWZOME! you know Lizard is so vicious. That is what makes him such a great villain. Lizard is a brainless, violent, killingmachine.
Second clustering may not be a bad thing in a Spider-Man movie. I mean the only reason the clustering sucked in Batman was... well here a a few examples...
1. in Batman 2 Catwoman becomes catwoman in the stupidest way possible. She falls out a window and seemingly dies... cats start to lick her and she seemingly come back to life as Catwoman. How stupid!
2. In Batman 3 Riddler uses some 3-D tv thing to hypnotize people... hmmm... stupid.... That is what I thought.
Now Spider-Man on the other hand could stay more with the comics with the villains that are in the Spider-Man movies.
Anyways here are some possibly great villains for Spider-Man 4.
Mysterio: Mysterio always is interesting and could provide a great fight with Spidey. The illusions stuff is perfect for a Spidey movie. Also A story can be provided with Mysterio alone. It would be in my view very difficult to have a villain such as Scorpion or Rhino alone in a movie as the one villain facing Spidey.
Sandman: An interesting villain that can provide a suspenseful fight for Spidey in any Spider-Man movie. A Sandman and Hydro-Man story in Spidey 4 would be good. they have actually joined together to become one once.
Silvermane: Silvermane could be in multiple movies. The possibilities are almost endless with Silvermane. Silvermane stories could work well with henchman such as Hammerhead, Rhino, Tombstone, Man Mountain Marko, or the Answer. Also there are possibilities of having cloak ad Dagger in a Spidey movie if Silvermane is in one!