I think one of the big complaints in Rifts is that the OCCs/RCCs are not balanced to each other. While I don't see this as a huge problem myself I guess I can understand how some people look at it. As the GM I usually let the players know what kind of game I'm about to run. I don't feel bad one bit restricting an OOC or RCC if I feel its not with in the power level of the game I want to run. You dont have to allow it just because its in the book.
As a matter of a fact I've been thinking about running a street level game set in chi town. With all street level characters. Imagine a group of bounty hunters ducking coalition patrols. Taking on clandestine missions for one group or another.
I recently picked up chaos earth. Its basically the prequel to Rifts. Set at the beginning of the end of the world. While a lot of the same tech is available the power level of the whole game is a lot lower. Its really a great way to run lower powered games. A lot of OOCs from bionics source book and other books that are considered underpowered for Rifts would be great for Chaos earth. I think a fun game would be to start players as SDC only characters. Sure military gear is out there...but you don't get to just start with it.