Tad,
Yeah, I also use wheels on trails, not all of them. Most portages are fine, more like roadways. But trails to mountain lakes, backcountry ponds, etc, are often little more than a bodies width. The wheels are constantly grabbing brush. Trails along and down to rivers are often shorter portages, but steep banks of roots and rocks can present problems. In the St. Regis area, for example, portages are less than 3 miles, generally far less, I do not use wheels there. On the Raquette River, I do not use wheels. The trails are usually shorter and they are often "improved" with rock lined drainage diverters to help prevent eroding the trail…they swallow wheels forcing a lift over these "obstuctions." Several water falls on a trip means long portages or rough rocky trails around falls, again, not conducive to using wheels in the narrow foot paths.
Of the wheels, tail mounted and center mounted, the tail mounted seem to handle rough trails slightly better, but don't turn as fast, but tag along behind you with no great effort. Center mounted wheels are usually wider, do not handle rough trails as well, but are more maneuverable. For good trails (there are a lot of old logging roads in the ADK's, example Moose River Plains) center mounted wheels handle heavy loads better, because the weight is centered…easy to drop your pack in the boat, too.
While wheels help at portages, they also weigh 2-3 pounds with larger bicycle wheels weighing much more (besides being awkward to stow.) A yoke weighs 10-1loz (wood and pads.) Lifting a boat and wheels over trail obstructions and anti erosion drainage channels can be more difficlt with wheels.
For sea kayaking, it doesn't much matter. These are often just paddles between campsites along a coast. But, landings can be nearly impossible on some. Larger waves and breakers can leave you soaked after hours of dry paddling. Wheels can rarely be any large benefit, but help you get off a beach in short order. But, on a dry day, they can dig into sand.
My boat weighs about 25 pounds including a spray deck, 9' paddle and life jacket. I built it myself for the purpose of exploring the ADK's. My pack weighs about 23# for about a two week trip (Food at 1.2-1.3#/day, base pack at 6-7#, a few comforts.) For 50 pounds it is not bad to carry, weight wise. But, the length can be awkward. In a fairly heavy wind, the boat is work. In gusty weather, it often blows me off the trail into the bushes. Wheels help a lot by lowering your profile.
I dissagree with this: "If you have large dia. wheels (like bike wheels) no path is necessary." Sticks, scrub, grasses can impede progress a lot. Off trail hiking with a set of wheels is impossible through large areas of the ADK's. In a very few spots, sure, it can work. But, generally, you need a good trail. The higher center of gravity imparted by bike tires will also mean the boat will tilt and roll easier, difficult over real obstructions. They need to be wider to allow boat clearence. So, they sort of cancel each other out, but the whipping of the front end if one wheel catches on a snag gets more difficult with increasing width. I have tried it. They actually require a better trail for using them. For general portaging on a scale of no trail to good trail: drag, yoke, tag along wheels, center wheels, and bicyle wheels are about the order of usage. Of course, this depends on a specific area, there *are* exceptions to every rule. In some wilderness areas, a ranger may object to them…you get a ticket. (They may be construed as a "mechanical conveyance" that are outlawed in national wilderness areas. Another ranger ignores them as you sweat pulling them uphill.)
Anyway, this is sort of my overall take on using wheels in the back country. I restrict bike wheels to longer portages over good trails where I can put them in the bushes, to be picked up when I return.