Kauai snorkeling accommodations are as spread out as the spots themselves extending from the north shore to the south shore. But luckily the island is fairly small and doesn't take too long to drive around. The snorkeling is somewhat dependent on the season, so you may use that to help you choose where to stay.
If you want a vacation with less rain, choose your accommodations in the Po'ipu area rather than Princeville or Hanalei. There are also accommodations in Kapa'a and Lihue which are more centralized between the snorkeling areas. You could also consider staying in Princeville or Hanalei for part of your trip and in Po'ipu for part of your trip. This would certainly cut down on driving times if the weather cooperates.
Kauai accommodations range from simple to luxury, but are not large in number. The majority of the accommodations you will find on Kauai are condos and they also range from simple to luxury. There are also vacation rentals and bed and breakfasts available. Expect to find the prices a little higher than other islands. Review some of the Kauai vacation rental options on TripAdvisor. It can also be useful to check reviews for hotels in Kauai before you book.
The north shore has some nice snorkeling and both Princeville and Hanalei are within a reasonable drive of all of them. Most of the north shore spots are best snorkeled in the summer. There are three snorkeling spots accessed from Princeville and there is not much public parking, so staying there could give you an advantage for getting to these spots. Princeville primarily has one area for shopping and restaurants and it is on the main highway at the entrance to Princeville. The St. Regis Princeville Resort is a luxury hotel here. The Hanalei Bay Resort shares Pu'u Poa Beach with the St. Regis. There are also numerous condos and vacation rentals available in Princeville.
Hanalei is charming and offers some shopping, other activities and restaurants. There are vacation rentals, small inns and bed and breakfasts to choose from in Hanalei. Also, west of town is the Hanalei Colony Resort with closer access to Ke'e Beach, Tunnels and Kepuhi Beach.
There is not much snorkeling in this area, but it is a good place to stay because it is between the two main snorkeling areas on the island. There is a lot of shopping and many restaurants in this area. There are bed and breakfasts, vacation rentals and hotels to choose from in Kapa'a. Kauai snorkeling hotels range from high-end to simple, like Waipouli Beach Resort, Castle Lanikai Resort, Hilton Garden Inn and Kauai Shores Aqua Hotel.
There are a number of nice snorkeling spots in the Po'ipu area and anywhere you stay you will have a short drive to any of the locations. The south shore spots are most accessible in the winter. Po'ipu is a resort area with shopping and restaurants and some luxury hotels, high end hotels and many condo rentals. For example, there is the Koa Kea Hotel and Resort, the Grand Hyatt Kauai Resort and Spa and the Sheraton Kauai Resort.
One last tip: if amenities like internet, swimming pool, fitness center, laundry facilities, on-site spa or restaurant are important to you, be sure you look for those while you are searching for Kauai snorkeling hotels so you are not surprised when you arrive.