I do this ALL the time. There is absolutely no structural reason to leave them. They are there only because of how they are cast, and the factory only grinds the least they can for an acceptable appearance. I remove most of the material with a die grinder, then spin them on a lathe and take off the minimum I can to clean them up and true them up round. You might be surprised how asymmetric the castings are. I also polish them up to a degree so they can be cleaned and look a lot better a lot longer. You can polish them up fairly matt if you don't want too much bling. I have done quite a few hubs, and most have small air bubbles below the surface which may be revealed if you skim the surface, so keep that in mind if you are expecting flawless polished surfaces when you are done. Conversely, aside from the obvious cosmetic and maintenance reasons, there is no reason to remove them. The weight you will save is negligible, and not worth the work if that is the only reason. By the way, TX500 and RD350 hubs bolt up identically. The 500 hub will take a second disc though, which is very handy if you want flip the fork to move that boat anchor caliper behind the fork leg and keep the stock speedo drive.