I was an elite D3 runner on an elite D3 team. I didn't start running until college, otherwise I would have had D1 and D2 options. My x-c team included two guys who went D1 and then came back to their hometown school for various reasons (one was at an Ivy League school and his aid package was cut (he didn't have a scholarship, but he did have plenty of other financial aid), the other was at an SEC school and got into legal trouble).
We competed against D1 schools on the track all of the time, and somewhat regularly in cross country. It was very cool to be one of the better runners and teams in D3, but still get to measure myself against the very best since we ran IC4As, Penn Relays, etc.
I do still wonder, however, what would have happened had I run in high school and gone D1. When I was running my best times, most of my workouts were done solo. The SEC guy ended up hating running because he couldn't live up to his high school hype, so he only ran cross country because he loved the guys. The Ivy League guy ran the steeple, so most of his workout were over barriers while I was running 5k/10k. Our 4th and 5th men simply couldn't push me or the Ivy League guy in workouts.
If I was on a good D1 team where I was the 4th or 5th best 5k guy and was being dragged along on each workout, could I have been in the low 14's, or maybe sub 14 instead of just under 14:20?
At the end of the day though, I wouldn't trade my experience in for a different one.