Any room temperature vulcanizing silicone (Smooth on) should be ok with the matter printer stuff from, lets say, Shapeways. Then, if your just messing around for yourself and don't care about production you can cast in resin. (that's the 'middle ground' in my mind)
If eventually you want a spin caster to make a spin cast mold, he probably could use one of your resin pieces as a master. Or you could always use the mold you were using for resin to make a wax model for the 'plaster' investment mold that will be used to make the bronze master.
I've been making lots of molds and castings with Smooth On products, after you get the hang of it it's pretty straight forward, just time consuming. I have made armor and 6mm figures with only a minor learning curve. I use a pressure pot, both when I make the mold and when I cast. Some of the compounds don't really even need that.
I just ordered some stuff from Shapeways that I made with a CAD program (Alibre). The only issue I have had is Shapeways 'takes their time'. I haven't made any molds yet with them yet but will in the next week or so. I don't however see any negative issues in doing so at the moment with the RTV silicone mold compound.
