In the past trail maintainence was done mostly by some local volunteers. I don't remember exactly who but they were somewhat organized. The Tower Tr. was relocated around the long slab and many trails were newly blazed. Middle and North get less attention. The trail down the east side of South is maintained by a local MTB group, maybe check the NEMBA site.
Most of the efforts of the very limited park staff is focused on the beach side of the park although there is a bunch of reveg. and conservation activity going on by the popular climbing spots around Round Pond. The back side of the park remains very undeveloped and there is a lot to said for that.
You can contact the park manager for more info: 895-3031
Bob