That is a heck of a deal to get an MTH BB for $500. I'd jump on that. And if you don't want it just you let me know.
I agree with what's been said. I don't generally run 1:29 cars with my 1:32 stuff either because of the size difference. I did go with Bachmann coal hoppers because their physical dimensions fit both 1:29 and 1:32. I do run Aristocraft Heavyweight passenger cars behind my 1:32 Challenger but it has been said those cars are probably smaller than 1:29 in scale.
1:29 just has wow factor that's hard to top. I'm like Pete, I never get tired of looking at my USA BB, it such an incredible piece. I'm also like Chuck, I enjoy running my MTH BBs because they are easier to handle and am less scared of damaging them. Another thing going for my MTH versions is the sound... I almost prefer them for that reason alone.
Either way I still enjoy both.