Siennas- what the hecks up with your...?

I haven't noticed that. If you get aluminum wheels that won't be a problem. I know here in Chicago if you hit a pot hole just right it can knock a hub cap off. They can even dent an aluminum wheel to the point of cracking it. If you need to replace a hub cap, there are web sites devoted to that, but they are all used. The dealer can order you one for a small fortune.