There is such a thing as too many rivets: when the inspectors start having to worry about your metallic wheels.
1 Though FIRST doesn't like hard things in contact with the carpet, they've been reasonably lenient with the fasteners used to secure tread to wheels. (Consult the 2012 rules for details.)
Edit: If you're interested in a bit of history about metal on carpet and tread fastening, see
this thread.
1 I long for the days when those were allowed.