Very good advice David, I like your pressure pots what are those made out of/from? I recognize them, but can't think of where I have seen them! I made a pressure chamber out of large diameter PVC pipe with fittings and it worked O.K., but those look superb and can probably handle much more pressure!
You are correct that most Die casts if used for casting will probably need some reworking/recasting for mass production and I have yet to see an ideal casting material for 1/43. The resin that the 1/43 model guys use is too brittle and some of the more flexible resins are too soft and don't hold their shape. Smooth-On has a couple that I think most guys use and they do O.K., but allot of guys want glass and interiors and maybe don't appreciate just how hard it is to cast something like that in 1/43 and have it stand up to normal slot car abuse. The A & B pillars are soo thin!
One of these days I would like to try casting the whole body in a clear resin, then just mask off the windows when painting; I believe this would be ideal for 1/43 if you could find the right material. The problem with clear as you know is all the things you mention like cost, cleanliness, etc. go double when you are casting in clear and you HAVE to use a Pressure pot. Slush casting won't really work for clear.