Thanks again for all the advice. Trip completed, here's a few thoughts:
1) It's amazing to have a lake as big as Kintla motorboat-free. I'm not sure there's another lake that size in the continental U.S that can claim the same. And to have one that beautiful to boot...
2) The trail between the lakes is a grunt, but I'm sad I didn't try to portage my inflatable kayak over. Paddling into Upper Kintla's lobes would have been beautiful.
3) A big trail crew was at work when I was there July 19, so things should be in good shape for the rest of the summer. However, the route up to Boulder Pass remains as brushy as any trail I've walked - shoulder-high on a 6-3 man.
4) We had light winds and 1-foot whitecaps coming and going, which made it exciting/tiring for the kids in the boats. For what Kintla can dish out on a cranky day, check this out:
http://www.wavelengthmagazine.com/1999/as99kintla.html