I agree with Kodama above.
I don't have both, but close. I own kayaks which I use for spearfishing and a boat (23 ft Radon). One of the big benefits with a kayak is being able to launch areas I can't with a boat, even an SIB, due to the shoreline (i.e. rocks and reef mainly). I've also owned some of my kayaks for 25 plus years and they're still going strong. I'm not sure how long SIB's are reliable for, but something you can look into.
For storage, I can fit quite a bit on my kayaks and I would need probably a 14+ footer SIB to start having more room with that.
When I dive, it's easy for me to pull up to two kayaks along when swimming along the coast. Depending on the SIB size, it may be more challenging.
I've paddled or peddled with my kayaks over 9 miles round trip comfortably and could go more. This is also dependent on physical condition and whatnot. If you're unsure, take a look at the foot pedal driven kayaks as they're easier on the user.
Wind is a factor and can limit you going out on a kayak or how far you paddle. What a little nicer with a boat is you can power through the wind, although rough. Some guys here get lost at sea because of the wind, so I'm mindful of that. Just carry the proper safety gear no matter which way you go.
Diving off the boat is wonderful and more comfortable. In my specific case, there needs to be a driver at all times and I'm always concerned for how the pilot of the boat is doing, if the seas are rough. I don't like worrying about all that. In any case, you can cover more ground and in some cases, get to places very hard to with a kayak. Just depends on your area. I honestly wanted a jet ski for diving, but the limitations here can be discouraging.