Not 40 seasons (that's one hell of a tenure) but I was at Abilene Christian (Smith) for 20 before I moved up to D1.
You do get an emotional attachment to a team after a while, but if you're itching ---- and I understand that itch --- you need to pick your destination and just do it. Don't look back. Even if your new team is crap right away, you have the coaching experience to turn it around.
I had an A+ and a NC at Abilene during those years. I liked D2 so much that after I left ACU for BYU D1, I went back to my old server (Naismith) and picked up a mediocre D2 squad just to play with. Took my lumps that first season (15-13) and I'm taking my lumps at BYU too, but the fun for me is in building my own program.
Go for it.