Amateurs, except for the tennis players, the football players, and the bicycle riders. All of which are the big name stars who get paid to compete in other dedicated tournaments. I'm sure there are others too but those are the most promoted sports.
I don't think the ones above get paid for the Olympics though.
Regarding compensation, it depends on the country, but I think many will get a bonus payment for medals or good performance. But anyway, the real money lies in advertising deals that athletes can get once they become big names (except for countries that have other types of compensation systems, e.g. North Korea).
So then there is absolutely no point in watching. Well, not until they start the doping league. (Should we debate whether the current one is?)
Even if you like the competition those seem like strong reasons not to watch.
I personally think that if you are going to allow finely engineered shoes, poles, javelins, boats, balls, bicycles, then you should allow finely engineered bodies.