I was thinking of an open sights only restriction - personally I don't think scopes make you a better shot (at 25 yds.). I use open sights, so if thats the consensus, it's fine by me.
Using as little equipment as possible makes for a level playing field. Using out of the box, no optics firearms lets the other people compete. You don't want someone competing with a eight inch barreled coyote gun with a ten power scope.
I had a discussion with a Highpower Rifle Master and I mentioned that I saw more cheating in IPCS and IDPA than I ever saw in Highpower Rifle.