I feel for the riders who've trained all year to get as fit as they can, spent a shitload on getting the bike just right and raced all season to get that 'racers edge' who get beaten out of the placings by a hired gun riding their Uncle Bobs bike for a one off bit of a giggle. I agree that there's little we can do to stop them but it doesn't seem very fair to me.
Whilst I completely understand what you are saying Firko, I don't see the difference between the "hired gun riding uncle Bob's bike" and the retired A Grader or international hired gun such as Belly or Deakin or one of the King boys from NZ showing up on someones bike and smoking you as well.
I guess the only way out of that sort of issue is to have class racing like they do in modern racing .. you know ... A Grade through to whatever grade it goes to now (C or D?) so that you are competing against others that are close to your level. Of course I am not suggesting we do that at all but that would resolve the problem you mention above.
Me? I just want to ride and do the best I can on the day riding bikes that mean something to me. I don't expect, nor do I receive, any trophies and if I was in the sport for that then I'd be very disappointed .. as would most of us I think.