I've been experimenting with GetTotalPlayerStrength. It seems to return the number of combat vehicles a player has. Note that it DOES NOT count Guard Posts.
I guess you could use this to tell your AI to prey on a significantly weaker player, or to strengthen its defenses if it's outgunned by another player. There are a few problems though, because there's no way to tell what kind of combat vehicles or weapons another player has (as far as I could tell anyways). So it could mislead your AI into spamming Laser Lynx and sending them all on a suicide mission against a bunch of ESG Tigers...
I assume GetPlayerStrength does the same thing but at a specified location.
A test DLL is attached. It will output a file (GTPS Test Results.txt) which will tell you your initial strength level (zero) and notify you of any changes (and at what mark those changes occured). I'll also upload the source to the SVN, for whatever reason. It runs in normal OP2, even though I put it in MT2\Colony Games.