cz, I appreciate you explaining more, but I would have to see it in action to properly advise. It seems this set could work as Google simply filters out duplicates.
As for blocking spiders from your cart, this is also a depends questions which an example page(s) would be helpful before saying yes or no.
I am personally not a big fan of blocking spider from content. I also dont believe in something called"
PR hoarding" where it is back to link out to your cart if they (SE's) are not going to index it properly.