I agree w/ 1) and 2). However, nothing with unpaid endorsements makes them different - LinkedIn is a place where we can exchange (meaningless?) unpaid endorsements as long as we don't compete w/ each other too much.

That's why PageRank worked on the web - it is very robust to this kind of abuse. If you gave away as much 'weight/sats/etc' as you gained, then you're where you started. Only an asymmetry in the final weight distribution will show who is actually more popular, not a plain count of local events/links, which are easy to fake.