If the computer has less than 3000 credits, it will 'try to spend money more conservatively'. There is a setting for this.. try lowering it. Also, there's an easy way to have the computer build more refineries: simply make 2, 3 clones of the standard refinery and set the Techlevel to -1, so as a player, you can't build them. The computer doesn't have this limitation, it will always build the building as long as they have the right House to be the Owner of those cloned refineries, and the AIBuildThis=yes tag is present

Interesting findings about MultiplayerAICM btw, i never bothered to look at it that closely.
And, welcome to TiberiumWeb
Please contact me on msn if you need me for anything, thanks.