My youngest plays in the HCL. Mix of JUCO - D1. A lot of kids from the Ivy's as well as HA D3s. Where I've noticed a difference is in speed and athleticism at the MIF and OF positions. That said the D1 players here are either very young (incoming freshmen or sophs) and/or at the smaller D1s.
The reality is in you're probably not going to see or at least shouldn't see a huge difference in skill difference at these smaller collegiate leagues. Every once in a while you'll see a kid who got his contract pulled in the Cape that comes on is sitting 93 which is fun, but also rare.
I'm sure geography has a lot to do with it as well. If a kid lighting it up in our league, there's a good chance he'll leave and go play in the NECBL or even the Cape.