Only done 4 dives in Coz, but am making my third trip to Bonaire next month, lets see if I can answer some of your questions...edit- my one trip to Coz I roomed with georoc01, so he can say if the Coz diving was typical or if we did some of the not so spectacular reefs there. They were nice for sure, but nothing compared to the reefs in Bonaire...
1. Great diving with lots of available dive ops
The diving, IMO is far better in Bonaire, there is just so much more to see and you are not drifting over sand going from coral mound to mound. Also, if you see something that you want to hang out and watch a while, there is no, or very little current, to blow you off the site. Also, there is no limit to how many dives you want to do in a day. Just dive all you want, it is shore diving unless you want to charter a boat to go to Klein...
2. Extremely friendly residents...the locals are always helpful and polite.
They don't get much friendlier than in Bonaire. I have been in the back country, as far away from the tourist areas as you can be, all hours of the night, drinking with locals, some of which were dirt poor, and never felt threatened at all. There is crime to be sure, and never leave anything of value in the car, but my experiences on Bonaire have been nothing short of spectacular when dealing with the locals.
3. Cheap eats...two words: Comida corrida!
If there is a cheap and good place to eat on the island, I have not found it. Sure the road side stands, or "snacks" are not going to drain your wallet, but the cleanliness of these places may cause you to get sick if you aren't used to it. Also I found most of the choices to be very greasy, not always good for diving. The restaurants are all top shelf, but the prices are top shelf also. To compensate we eat most meals in the kitchenette from stuff we bring with us, and only eat out once or twice.
4. A safe atmosphere...we have strolled around the side streets at night with the same precautions that we use anywhere. (Staying together, staying sober, avoiding dark streets, alleys, etc)
I strolled the back dark alleys as drunk as I have ever been with no worries. Granted I am 6'5" and built, but some of the locals are bigger. Also when you are falling down drunk you are not a threat to anyone. The locals were great fun, and nobody even tried to rip me off. In fact there were times they were buying me drinks and I felt like I was taking advantage of them! Probably not the typical experience but it does illustrate the friendly nature of pretty much everybody on the island.
What are the pros and cons of Bonaire in relation to Cozumel?
For me it is cheaper and easier to get to Bonaire as opposed to Cozumel. My primary vacation buddy is a long time lover of Coz, but a recent convert to Bonaire. I have only made one trip to Coz and that was blown out by a hurricane. I have heard wonderful things about the place, but honestly I think the diving is better in Bonaire, it is certainly unlimited, and the fills are all 3K plus.
The West coast is all easy diving, if you don't like the ripples in the South, just drive North for bath tub conditions, or vice-versa. If you want some excitement, then hire a DM to take you out on a shore dive in Lac Cai, or take a ride with Larry and dive the East coast. Just be prepared to be thoroughly waterlogged by the time you crawl onto the plane for the flight out...