The unit limit isn't your computer, it's the game. It seems to be related to the amount of graphics objects or XBF files, as adding new explosions and new bullets put me over the limit as well as adding new units. You can increase the number of units, bullets, or explosions you can add by removing others, such as incidental units. This limit seems to make huge mods with lots of new stuff (and all the old stuff too) impractical. However, instead of making one giant mod with everything in it, you can make more than one mod, each different, so when players get tired of playing one, they can play another one to keep the game interesting. Of course, this calls for someone to write a mod management program, so players can easily select the mod they want to play instead of having to backup, copy, and keep track of a bunch of files.