I would have thought it shouldn't be too hard to have both modding and no 'cheating'. Just have a few rules about how tradeoffs occour.
If you've used the CAM, you know there's a relation between the volume of a building and the building stage and capacity. Just use this kind of rule to work out what your modded object does.
So if you want to create a box factory, you build the model, import it into your addon maker saying it produces boxes. The maker then measures the volume of the factory then the maker presents you with a series of interlinked sliders:
Workers in, Polution out, Box production rate, worker education level.
The range of production rate is worked out according to the volume, and if you slide up the rate then the polution and workers in also slide up.
You can lock the production rate if you want, which then restricts the range of the other parameters. You tweak the sliders until you get what you want, and then the maker spits out an addon file. The addon can then be shared using whatever mechanism maxis comes up with.