There was a group of us who built CAPs frequently back during the series "hey-day" that toyed with all kinds of "tricks" to conserve memory. I like the theory in the spoiler you posted ShutMeUp. What has always baffled me is why, when raising and lowering ground: if I raise or lower the ground, if I immediately revert that ground back to the default level, I gain no memory back. Well that's one thing, but I digress. We would typically utilize pre-made objects such as buildings to create pseudo walls to help conserve memory. I never did a full analysis of what/which pieces used how much memory, but man a comprehensive tutorial on this would be cool. I've forgotten, by now, more than I remember on space saving tips...seems like using quarter-pipes instead of pool pieces save memory and then use the rail tool to make a grindable lip above the q-pipe.
I think the master of tricking the editor back in the day, better than almost anyone I ran into, was EvilGod. He had that crap dialed. Hitstun was pretty good too- he loved the stack and merge glitch, and created some pretty cool stuff with that technique.
At any rate- back on topic: pre-made templates are a cool concept. THPS5's editor used this notion. Because the THPS5 editor was so glitchy I didn't get to play with it enough, but I did like the template idea. I could see utilizing these that you have come up with for CAP Building contest and the like. Good stuff!