I'll confirm the need to upgrade to the "superior" room at Casa del Mar, but would also point out that those ground floor rooms at the back of the hotel are not the only "standard" rooms, if they are "standard" at all. The entire back side of the hotel that faces the jungle are standard rooms. They're very small and don't have a balcony. You want a balcony if you're diving. Also, CDM has a pier for pickup too. They don't charge anything to be picked up by other ops.
There are a couple of close dining options other than the CDM restaurant itself, namely Ernesto's and Paprika. Both are less than a block from the hotel. Since the exchange rate is so good right now, taking a taxi to town for supper isn't as much of a factor, but CDM is a loooong walk to town. Scuba Club is much closer to town. Getting a taxi from CDM is extremely easy. Most of the time, we just walk down the steps from the restaurant and we have a taxi in less than a minute. There's almost always a few taxis right across the street. One nod, and they u-turn and are in front of you in about 20 to 30 seconds. Even if the desk calls one to pick you up at the lobby, it's rarely more than 2 minutes until you're climbing in.
I'm not sure how many divers are on the Scuba Club dive boats. I could be wrong, but I think they're big boats as opposed to small panga types? The last I heard, CDM's all inclusive package was $42 per day per person. You order off their menu and I think there's an upcharge for a couple of the items, as I recall, the seafood platter and the lobster carry an upcharge. It used to be that if you booked your vacation through Delta, breakfast was included. I don't know if that's still available. CDM opens for breakfast at 7am.
Scuba Club's all inclusive option/s seem nicely dialed in. It doesn't include alcohol and if I recall correctly, you can do breakfast, breakfast and lunch, or all three. Another smart thing they do (imo), is that you order what you'd like for supper, at lunch. In any event, they're preparing your supper fresh and keeping their food cost down. Smart. I've never stayed there and wouldn't as it's not the right fit for me, but there are some nice upsides to Scuba Club Cozumel.
If you choose Casa del Mar, I'd be inclined to dive with an outside dive op. Those that leave from downtown, Deep Blue, Blue XTC, Aldora etc, will pick you up at the pier, but I know that some other ops that leave from the marina will still back track and pick you up at the pier. CDM is the opposite direction of the marine park, but very close. For instance, I think Dive with Allison will pick you up at the CDM pier. I've seen her there many times. CVchief would know for sure. If you stay at Scuba Club, you dive with Scuba Club, which is no doubt a fine choice.
What I like about CDM is that it splits the difference between big sprawling resort and small hotel. The grounds are very nice. They have a pool with a swim up bar and a hot tub. The restaurant's menu is small but I have many favorite items. The rooms are clean, etc. I think a taxi is about $5 US one way to town. There's shore diving there. The hotel is a triangle, and the best views are on the 3rd floor on the leg that faces northwest. If you're on the southwest, you're seeing trees and cruise ships from your balcony. From the furthest room on that 3rd floor, it takes me 50 seconds to get to the bar/restaurant.
One other note. If you choose a dive op that leaves from a downtown pier, or that provides "courtesy" transportation to the marina, you have a little extra time for breakfast, etc, if you stay at CDM. So for instance, Aldora leaves from downtown, very early, well, you've got an extra 15 minutes. Same with shops that leave early and provide transportation to the marina. When I'm on vacation, I'm there to relax, and having limited time for breakfast doesn't fit my bill. The op I use, Deep Blue, leaves from a downtown pier at about 9am. I have all the time in the world for breakfast, getting my cameras together, etc, and for watching the other divers who dive with ops that leave early, eating breakfast in neoprene and moving fast to get done and on the pier for their pick-up. Fine for some, not for me.