I think filming your own stuff can be a good way to get noticed (well, I know it is), but I think if you're going to make your own short films or whatever, you should write specifically for that purpose, and use those shorts as calling cards to get interest for longer works.
I'd definitely advise against filming even part of a script you'd like to see done professionally (unless you're doing it for your own purposes, to see what works).
Unless you splash out on tip-top production values, I think that any whiff of "amateur" would prejudice a producer, even subconsciously, against your project.