The weather shouldn't be an issue for dive sites directly off Seven Mile Beach. The West Bay sites can get washed out in the winter months. If the weather cooperates for doing either the boat going straight out from or north of the West Bay dock or shore dives on Turtle Reef (or Hepp's Pipeline if you stay at Coconut Bay) - they are all fantastic dive sites. The mini walls have so much beautiful life scooting around. It's my favorite place to dive. The sites farther south from the West Bay dock off SMB are generally a little overdove and IMO a little boring compared to the sites closer to West Bay. Our experience last trip was that the dives on the North Wall and out around the East End are longer boat rides and deeper dives, so maybe save those for next trip if you're looking to ease back into diving.
I loved Bonaire (both the diving and the people/topside activities), but my husband thought it was very boring diving. It was also very easy diving. Some of the sites are harder to get into the water from (i.e. 1000 Steps is exhausting), but the vast majority are a very easy entry and exit bookending a very easy dive. The topography is pretty similar on many dive sites. Klein Bonaire was a short boat ride away to get some varying topography. The reef in Bonaire is generally gradually sloping and not a wall dropoff, so I think you would like it. There are SO MANY fish there - it's incredible. We didn't see much big stuff, though. I wouldn't worry about crime there. We left cheap stuff in the truck (sunglasses, white t-shirt) and it wasn't stolen. Even if it had been, we knew it was a possibility and wouldn't have missed it. We didn't feel unsafe at all while we were there. Everyone we encountered was friendly and nice.
As far as Bonaire vs Grand Cayman in a head-to-head, GC wins with me hands down. We plan to go back every other year or so. The water is just breathtaking and we like having varying topography (swim-throughs, canyons, walls, mini walls, wrecks) more than easy access to tons of cheap diving like Bonaire offers.
Do you take anything for motion sickness? I have a strict Dramamine (Bonine does not work for me) regimen I need to follow the entire week we are diving or I am chumming over the side of the boat anytime I'm topside (and chumming through my reg sometimes when I'm under
). Dramamine doesn't make me drowsy, though, so that's a big help. PM me if you want to hear my regimen! It worked for one of our friends earlier this month in Saba who had trouble getting the seasicknesses under control on boat dives.