Is it almost empty atm so the flag has become a necessity or it's purelybecause of the abuse and the purpose of rewarding great contents more?

It can't run empty. What comes in goes out, if someone gets more others get less.

are we trying to be appealing to the masses who are mostly not cambridge/ivy league literate or the later?

All of them - the masses would profit from having a source for ivy league content so to say, but they wouldn't (and shouldn't) make a living with shitposting.
How the value plays out depends on a lot of factors, and I can't honestly forsee that. We have more chances for it to rise if people don't think this platform rewards people for having something in their wallet I assume.

How do we know that the circle jerks would not just switch to upvoting the trending knowing that they would earn curation rewards on that specially if the trending posts has much or am I seeing this shortsightedly again?

Not everyone can get high rewards by upvoting trending. As soon as something is on trending, the curation rewards are bad, as the high rewards go to those who voted on it first. Trying to predict what might become trending is part of the concept, but if everyone jumps on the same authors that becomes highly competitive. It's better for your own rewards to vote on something small that becomes big later, than something that is already big. That also kind of answers your next question, there is no hard limit to adding support, but for yourself it's always better to find the next trending post instead of piling onto one that's already there.