Here's what I learned: if you can't write a gripping one-page synopsis of a screenplay, your plot points aren't very dramatic.
Two of the scripts proved pretty easy to summarize and make dramatic (well, as dramatic as you can make something when describing it in one page). But with one of the stories I kept writing out the dramatic moments and then having to describe why they were turning points when, on the face of it, they didn't sound very dramatic. And after a bit of head scratching I realized that I had simply failed to dramatize the moment adequately.
I just bought and re-watched "Get Shorty", and there's this moment where Gene Hackman's character is trying to explain to Chili Palmer why he had blown a wad of borrowed money in Vegas, and Chili cuts him off with something like, "Harry, you did something stupid and you're trying to make it sound like it wasn't stupid, and that's hard to do." It's a great summation, and it's exactly what I felt while I was trying to summarize my own story. What I ended up doing was writing the best single-page version of the story I could, then altering the script to match the better description. Interestingly, this was a script I've never pitched verbally and I wonder if I wouldn't have fixed the problems after I'd failed to pitch it well. I also think the single-page version was even better than doing a verbal pitch because the one-page limit pressures you into presenting just the skeleton, and if a story isn't interesting in that form, no amount of window-dressing is going to help.