Why did you choose Aruba and St. Lucia? They are so different from each other. Aruba is dry and arid...not what you expect a Caribbean island to be. St. Lucia is quite lush and apparently does not have the clear, turquoise water that most Caribbean islands have.

From what you described, Aruba would probably be the better choice of the 2. It's a safe Island with 2 great beaches, tons of dining and bar options, and excellant public transportation. You'll probably want to look at the Eagle Beach area, which is quieter. The Divi, Bucuti, and Manchebo get good reviews. The lanscape is flat, arid and dry with a few palm trees.

St. Lucia is very lush. The beaches are a darker sand and the water a deep blue. Most everything is spread out and people complain about the windy roads, which we didn't have any problem with. You'll probably want to stay in the Rodney Bay area to be close to dining options.

The water is very clear in St Lucia (except for couple bays), it ranges from dark blue to emerald green colour. Because the sand is darker is some areas (mainly the south around the Pitons), it does not mean the water is not clear. Here are some photos:-

http://www.tripadvisor.co.uk/Attraction_Review-g147342-d150064-Reviews-Anse_Chastanet_Beach_and_Reef-St_Lucia.html

I do agree though that picking these two islands is strange, they are chalk and cheese. If you choose St Lucia and you go to the Pitons area, I would definitely recommend AI because the area is remote. There are some very lovely hotels in this area that meet most of your requirements (except museums). Most AI hotels have more than one restaurant or offer a variety of cuisines, personally I always go AI in St Lucia.

If you stay around Rodney Bay/Reduit Beach, there are plenty of dining options but this is a lively area with lots of young people partying. The sand here is lighter, the beach can be a busy place (not Aruba busy though).

For a first time visit to the Caribbean, I am not sure Aruba will be the image you may have in your mind as to what a Caribbean island should look like. If you can get past that, then it also offers everything you need (although it is more crowded than St Lucia), you do not need AI because there are so many dining options. Beaches are lighter sand than St Lucia and the water is lovely, snorkelling is not bad around Malmok Beach.

Are you open to other islands, example Barbados? It's a great first time island, it has beautiful calm beaches on the west coast, has museums or at least historical sites of interest, beautiful landscapes along the windy east coast and south of the island, lots of restaurants (but you may need a car). Snorkelling is not the best, but if it is your first Caribbean visit you have nothing to compare it to, there are turtles though.

I would also look at Frommers online and narrow it down, then go to tripadvisor.com and get the real reviews from real people!

If you are looking for a non-all inclusive, then you may want to try Renaissance Aruba Resort in downtown Aruba, it is off the "tourist" strip, has it's own private island which they boat you to and from and it is steps from many different restaurants and cuisines. I stayed in the Adult's only section of the resort, there is no hot tub, but they have a fitness facility, the beach is on a private island which is divided into Family side and Adult Side. The beach is near the airport however so you do hear the planes take off once in a while. We had a fabulous time. You can see my full review at my travel blog http://dreamtravelmagazine.com/hotel-reviews-renaissance-marina-aruba-resort-casino. If you have questions feel free to send me a message!