AllenG,
Sorry it took me so long to reply, as to the answers to your questions:
1. There are not any special spots of interest right on CA1. Everything is from 1/2 hour to 2 1/2 hours off of CA1. Volcan Arenal, Monte Verde Cloud Forest Etc. However the drive itself is breathtaking.
2. The visibility depends on the dive. It can go from 20 to 60 feet during one dive, it just depends. I have been told the visibility is better during the rainy season.
3. I was there at the end of March, 80 degrees at the top and 63 at the thermocline at 60 feet. You can get away with a 2mm shorty and be very comfortable.
4. The boat trip to catalina was about 1 hour 15 minutes. The Bat islands are a lot further and most dive ops run overnight trips to get there. I did not go to the bats so you might want to email the local dive shops.
5. The local dives I went on were great, but the visibility was a little better at Catalina. The local dives have a lot of stuff to look at too and from what I was told, it is not uncommon to see both Mantas and Whalesharks on a local dive. I did not see any however.
The diving is really good. It's not the clarity of the carribean, but you will see more wildlife. You may even hear the distant call of a larger whale.