"Actually it appears MTH just left off the tires to save a few cents."
I always thought that the reasoning was electrical pickup; the flanges do indeed do part of the connecting on our locos, but I imagine that 4 wheels with "rubber" tires on them would have given iffy performance at best. 2 smooth and 2 "tired" might have worked.
My ROW 3RO brass "Docksider" has no traction tires at all. It pulls anything that an 0-4-0 should be asked to do. If you find one of these on eBay it would make for a nice upgrade from the MTH. I think that they are both over-scale, especially the RK.