I know what your saying about slop (too much is bad) but it is not only the lesser cars that have it bad. I run Yokomo at the minute and I bought a brand new GT4R 6months ago. When I built it I was fit to make the car dance. The slop in the front end was so bad that I couldn't get a true reading on the set up station.
The servo saver in the Yokomo has a lot of slop and the upper front wishbone can move sideways (away from and towards the chassis). This gives you a real headache when setting up as you never get the same reading from both sides.
What I did was use a Mugen Servo Saver and Tie-rods for the steering and to cure my wishbone problem I got some brass hollow tubing with inner diameter to match the hinge pins and squeezed it into the bulk head mounting points. Now, I have a fairly slop free car that is easier to set up.
As for making custom parts, I do this also (with Carbon Fibre mainly). My current project is to convert the Yokomo steering to the same setup used by the MTX3. I will keep you all informed.