This may not be what you want to hear; but it’s true.
I’m not saying a work of utter genius won’t blow all its competitors out of the water; but as I’ve mentioned before, most of us produce work of a very similar quality. Genius is very rare.
Think about it: you receive a sketch which is good; it’s funny, topical and easy to perform. It goes on the pile. A few days later, you receive another sketch on the same subject which is just as funny, maybe even a little more so; but you’ve already started rehearsing the other one, and it isn’t that much different really. So you stick with what you’ve got.
Any sketch which gets there second, or later, has to be considerably better in order to replace the first one.
The same applies to screenplays: a production company looking for scripts will be easier to impress earlier rather than later. As the ‘maybe’ pile grows, it gets harder and harder to get added. The odds here are probably better than topical sketches, at least your script will (hopefully) have a different story; but it’s still got to be better to get there first.
Or maybe it doesn’t work like that? Maybe the quality of the majority of scripts is so poor, any diamond shines, no matter how late in the game? I don’t know, but I wouldn’t be willing to risk it.
For me it’s all about maximising your chances. I stick to standard screenplay format, even though I know standards in the UK aren’t as strict as the US, because you never know when you’re going to come up against a truly anal reader. I don’t want to get marked down for some minor margin infraction, why run the risk when the rules are easy to adhere to?
Yes, you need talent, skill and the ability to spell; a good story, great characters and killer dialogue – those are a given. If you’ve got all these, getting a script in earlier may not help; but it certainly can’t hurt.