It can be as rugged but it will weigh almost as much in order to retain cosmetic appearances. It's not easier or harder to fix. Once you know how to fix stuff you fix it. A standard built Penguino will weigh about the same as a Current Designs Vision and less likely to develop cracks on hard landings as the Vision.
"When Pygmy came out with the 13 ft Pinguino, I thought it looked good but a little short for good tracking."
Make up your mind, do you want a light, efficient day kayak or do you want a heavier load carrier? Beginners overrate tracking because they aren't that skilled keeping a kayak on course. Getting a longer/bigger kayak doesn't mean it'll track better, it might mean you'll get blown around more as less of it is sunk in the water.
"Then they followed up with the Pinguino 145 but with a 25.5" beam, it's still a little chunky. John Lockwood says it will "keep up" with faster boats, but it's cruising speed is still at the bottom of the list."
Beware evaluating kayaks on numbers. You aren't paddling numbers. If you want a light kayak get a small kayak. If you aren't planning on carrying 75lbs extra gear don't get a kayak where you are carrying around extra windage and weight.
"I just question whether it's as practical a proposition (cost-wise) as building a longer boat. Still spinning my wheels here...."
You build a kayak because you want to build one. If you want the lightest/lowest cost kayak for day paddling in Maine get a Necky Manitou 13 and put a float bag in the bow. Seriously you are not going to get a practical benefit from a longer waterline kayak if you are not paddling faster than 3.5mph. It will take you at least 3months to build a kayak and the other costs will add $400 even if you have all the tools once you go through materials, gloves, sandpaper, paint,varnish, table/saw horses for building (crawling on floor is no fun).
btw, the water in Maine is cold, whatever kayak you get get dressed for the water and go through basic rescues with an instructor or club.
I've owned dozens of kayaks, taught sea kayak, built about 14, the Pinguino 13 is a good design. If you don't want to build, don't buy a kit.