Happy Hound:- You sound like me at a script workshop! Originally I did write it as a screenplay, but then switched it round when someone asked me to adapt it for stage (which it was then performed as). I then found I prefered the the sparseness of this version (minus camera shots, close-ups, suggested angles, etc) and left it as it is.
Hand on heart, I feel it communicates more directly to the reader in this format. If anyone feels they can cook up the £10,000 or so to shoot it, I can easily pop across a version that has the tabs in all the right places!