A Cessna 172 can be a great airplane for a LOT of missions. Like any other airplane, you have to consider the mission before tackling it, but the difference is more often the PILOT rather than the airplane.
A Sportsman STOL kit is a good (but fairly expensive) mod to the 172 (or any other Cessna).
If you already have the Lycoming engine, as in a later model airplane, you are ahead of the game, but even the O-300 does fine.
I guess I'm the odd man out, cause I LOVE electric flaps, compared to the manual flaps. Sure, you can "pop" flaps with the manual, but just prior to touch, you can reach over with your right hand, and punch the flap switch to "Up", and the airplane will settle nicely, with no float. Try that just before touchdown in a manual flap airplane. You'll find that guys driving 206/207 airplanes do that pretty routinely in short spots. Bottom line, learn to use the tools the airplane is equipped with.
On ANY tri gear airplane to be operated off airport, I would install a "temporary" piece of thick wall rubber hose around the nose strut, split lengthwise, and held in place by a couple hose clamps. This prevents the nose strut from reaching its fully collapsed point, and helps to protect the prop, particularly if your nose strut loses a bit of pressure. Keep that nose strut pumped up pretty tight as well. Protect that prop.
I would DEFINITELY install a Landes nose fork, with bigger tires all around. Two reasons: better prop clearance, and better floatation. Think gopher holes, NOT big rocks and long props.
Bigger engines are expensive, but great on warm days or high altitude. I'd look for an airplane with one installed, rather than do the mod, though.
Learn to protect that propeller and firewall. I've seen firewalls bent due to nosegear first landings. This is the weak point of both the 172 and 182. Learn to work the airplane, AND if mostly empty, always carry some weight (think survival gear) as far aft as possible, to keep the CG a bit aft.
Finally, as many folks have noted on many forums, the best modification for ANY airplane to be operated in the back country is to spend a LOT of money on flying it, and LEARNING to fly it. Go find folks who KNOW how to fly a 172, and learn from them. Then, practice, practice, practice.
MTV