Hey Scuba Man, you're definitely in the market for a sit-on-top. I can only assume that you might be using your kayak considerably for access to dive spots away from large boat anchorages or moorings. You'll be terribly disappointed if you try to load your scuba gear in a longer/narrower sit-in recreational kayak. There's just not sufficient holds for tanks, regulator, markers, weight belt, wet suit, flippers, and buoyancy compensators. The sit on tops are mostly designed for various purposes which include surfing waves, rough water, and even sailing with the right accessories. Sit on tops are also tremendously stable...dependent on the beam width you select. They are clearly intend for wet rides, with scuppers that drain water quickly. The scuppers can also be plugged for a drier paddle. Your gear would fit much easier in a sit on top with only a few bungee cords. There are actually some really nice SOT kayaks designed for scuba, and they might be worth consideration...if price doesn't matter too much. The biggest shortcoming is once again, as this knowledgeable group has stated...these are wet rides in turbulent water. Shuttling family to a dock for a bite to eat would not be much fun for the kiddies or Admiral. If you want it all...you might consider an inflatable dinghy and trolling or gas motor.
One more thing, although inflatable kayaks might address all your usages and are incredibly stable, they track terrible...making your voyage to wherever exhausting by constantly correcting port and starboard without a rudder or skeg.