Mark,

I've written three screenplays.  First, you should only query the agent.  Don't send the screenplay when you're trying to land an agent - just the synopsis. 

I usually don't do a lot of rewriting.  I do a lot of thinking about each script (usually takes at least 8 months to write) so I only clean up the previous scene before writing the next one. At some point you have to let your "baby" go.