Well, I have just read this whole topic and am going to take a gander at it.
Firstoff, limiting subs would make the High School game so much more enjoyable to me. High School varsity soccer is not a game where the goal is to get everyone playing time. We have rec league for that. The 2 subs per half and unlimited at halftime is perfect (I would suggest 3 per half however). Limiting subs would increase the competitiveness greatly. Like star said, players would be constantly challenging eachother for starting spots. Personally, as a high school player, I enjoy a challenge in keeping my spot. Moreover, I hate to be subbed, even when I am injured or extremely tired.
Also, I think that the games would actually be lower scoring with this type of subbing. If teams only get 3 subs, then the starters are naturally going to pace themselves better and not be so aggressive. The way we have it now allows the starting 11 to quickly score many goals on weaker teams and then be subbed out to rest, only to later release more onslaught.
Limiting Subs would slow the game down and create more strategy in how key players should be subbed. This would create a playing environment closer to the European style, which is what we aspire soccer to be like in this country. Am I right?