I had snorkled all over the world, but for some reason had never gotten my Scuba certification until last month at Utila with Captain Morgans. Here are some answers to your questions:
**I think diving is worth it. Honestly, I didn't see much at Utila that I hadn't seen snorkling...no sharks, rays, etc, but the underwater topography is fantastic, especially on the north side. The Halliburton wreck on the south side was great. Overall, much better diving for me in Belize (the Blue Hole doesn't disappoint.) I don't know if there is much snorkling at Utila....not so much at the dive sites we went to. The snorkling on the cayes was good if you got away from the main settlements.
**I enjoyed taking the course with Captain Morgans on the Cayes. Great fish burgers, lots of contact with locals, much more laid back, etc. It took me 3-4 days for the whole thing. If you're not diving though, the Cayes got boring for me real fast.
**I thought Captain Morgans was a solid operation overall...with a couple of big complaints. On the good side...great location....my dive instructer (Johan) was outstanding....equipment was decent....I had a great room at a place next door called the Lone Star, for $15 had a sunrise view and hot water. You can stay cheaper at the Capt Morgans dorms if you don't want privacy or hot water. Attention to safety, following proper procedure and minding the environment were outstanding. Complaints....on the dive boat half the divemasters and divers light up cigarettes constantly....sorry, but out on the beautiful sea the last thing I want to smell is someone elses second hand smoke...COMPLETELY UNACCEPTABLE to me...the operation I dove with in belize had a strict no smoking policy The other thing...late one afternoon I was taking the dive boat back to Utila town and the sea was VERY rough. A few of us were asking about life jackets, just in case and the divemasters said there were none and they joked that the empty air tanks would float. Now the boat was never in danger of sinking and we were only 200 yards offshore, but for a boat that goes out on the open sea not to have life jackets on board is also completely unacceptable....especially for an operation that was really very safety conscious. If you're a non smoker, I'd seriously ask about a dive shop's smoking policy...it would be a deal breaker for me.
**Hmmm, what else....I thought Utila town was OK....doesn't touch Caye Caulker in Belize IMO. Great room at Rubi's for $20.....complaints...the locals speed around the narrow roads on motorbikes, ATV's, golf carts and small cars. I found it very annoying. Also, I'm going to offend some people here, but Utila was very much a backpackers hang-out. A few too many chain smoking, hard partying, dreadlocked European kids for my taste. (I'm more of a "flashpacker") But of course the cheap prices cater to that crowd. Again, no comparison to Caye Caulker Belize...but Belize is much more expensive, so you get what you pay for.
**The course pretty much progresses at your own pace. I found it just right...certainly not too rigorous. The only "classroom time" was watching the videos..the rest was in the water or reading the book out on a hammock.
**Whale Sharks...hahaha....I was there from March 5-12 and there were no Whale Sharks....of course there apparently was a sighting the day I left and several more the following week. Obviously they don't arrive on schedule, so it's hit or miss. From what I heard, I wouldn't base a trip to Utila on the probability of seeing whale sharks (no matter how much all the websites and brochures promote it).
That's all I got for now!