By the time you're approaching New England (May I'm assuming), you'll likely want to cashier the overboots. But my memory still lingers strong from 99, a drought year, in which Massachusetts was still fairly marshy even in July. In damp spring conditions, I would expect you'll have to deal with considerable muck in many places. Even with seal skinz to keep your feet somewhat day, the mud entering your shoes will likely decrease the lifespan of both shoes and sealskinz.
In New Hampshire, the loose gravelly portions of the trail, which are common even below treeline, would have driven me crazy without gaiters, and I wore boots, not trail runners.
I admit I'm a big fan of gaiters and I wear them most all the time when I hike, but I HATE getting grit in my shoes. In mud, they are just about a necessity with low-cut shoes. I prefer the slightly heavier velcro types such as the OR Flex-Tex Gaiter or REI Mistral. They are water resistant, not waterproof, but do fine in muddy or gritty conditions. The Integral Deigns Event SHort Gaiter are waterproof and a bit lighter, but I found them such a pain in the butt when I used them hiking the COlorado Trail this past summer that I hesitated to wear them at times. If you'd like a pair, I'd sell them to you cheap!
But seriously, in the later portions of your though-hike, you'll likely find gaiters very helpful.