is there a relatively inexpensive touch-up paint that matches the OEM 16" silver wheels if they've been scratched or curbed?..

perhaps the silver touch-up paint for the Fit or Civic is a close match?

 

I'd bet that Alabaster Silver Metallic would be a close match. I had an ASM Element, and used the touch up paint to touch up the wheel on my ex-wife's Mazda5, which also used just painted alloys instead of the brushed and polished finish.