I get where you're coming from. I mean, you can very easily and successfully power a heavy, 30 foot sailboat with 10 hp. So now you're looking at a "light" 22 and suddenly it needs 90?
A few things to consider:
It's a planing boat. Now, I've been happy to cruise at "hull speed" for much of my life, and I still love displacement boats. BUT, when you (I) have a planing boat, well, it IS fun (and often useful) to be able to push the throttle forward and zoom along at 18-20 knots. Why might one want to?
a) You watched the weather but something unpredicted came up, and you'd like to avoid it as much as possible.
b) You are in an area where there is a fair distance between anchorages. This way you have more options (that you can get to before dark).
c) You cruise a local area and have limited time on the water. This way you can "zoom" to a wider variety of areas, even if you plan to take it slowly once you get there.
d) Emergency or etc.
Also....
i) Let's say a 9 hp will give you X GPH (or MPH) at a certain speed. Well, the 90 will do about the same, since it's just loafing along. Granted, the 90 costs more to buy and maintain, so if you never plan to go above the max speed of the 9.9, no reason to go with the 90. OTOH, if you have the 90 for occasional use, you'll still get the good "mileage" when you cruise slowly.
ii) You can still do some of your own maintenance, and when you can't (presuming you have a trailer and can tow), you can bring the motor (and boat) to the mechanic, instead of needing a service call in the slip. Anything above about a 6hp you probably won't be lifting off the boat unassisted, depending on you (I can handle my #45 5hp, but no way the 110# Honda 8 that came with the boat).
iii) A former dealer on the East Coast (Cutter Marine) sold quite a few 22's with a 50hp. I think they did plane, if not overloaded. But I would guess most were repowered with a 75+ hp. I guess if you're going to plane... just do it with adequate horsepower.
iv) If you are truly uninterested in re-sale, then great, one less theoretical person to please. OTOH, if you want to step in in a "sensible" way, you could perhaps start with a 9.9hp kicker and no "main" engine. If it works for you, great. If it doesn't, slide it over and use it as a kicker and get a larger engine (same if you want to sell and the small engine discourages folks).
v) But to me one of the magical things about the 22 (and similar boats) is that it will plane at low speed. That doesn't happen with every boat. I love gliding long at, say, 12 knots ON PLANE. It's slow and fast at the same time. Zipping along at 20-30 knots is not as fun for me, so it's something I only do if I have to (get to anchorage before dark, etc.).
PS: I have a (carbureted) 80 hp, which is really a 75hp in today's lingo. It's perfectly fine for me, even for semi-loaded cruising and at medium altitudes (4,000' or so). If I re-power, I might go larger, but I'd choose more on weight and alternator size.
I have also considered the Yamaha 70. It's a bit small for someone who emphasizes speed/planing (small block), but OTOH it's very light and might be that just right middle ground for you.