When I got mine with 47,000 miles, I was in the same boat. Although mine is not rare, I still didn't want to mess with an original car. I consider it preserving a peice of history.
Someday, I do hope to have the best of both worlds. I have the stock small block car now and maybe a big block 4-speed will be in my future. The next Monte will be a fun toy where I won't worry about originality.
Either way, do what you want with it. I'm glad to see that you drive it and enjoy it at least.