If had to slim down from 3 bikes to, one bike it would be a Cyclocross bike. My current cross bike, a Jake the Snake, is a dream. The versatility of a cross bike with eyelets is unparalleled. The eyelets allow me to mount a rear rack so the bike will double as a commute to work bike and race bike. The bike is very comfortable for longish rides, 50 miles, yet I can get down into the hooks and hammer it home on my local bike trail. The extra clearance allows for fattish tires and fenders if I need. Some bikes might accept tires as fat as 40mm for a fast comfortable ride. When you go to check out bikes make sure you can get the bike up on to your shoulder as well as a proper ride fit.
The bike still remains a race bike, and it will get plenty of use this season. I’ve done a couple of crits here and there, and a few MTB races. I would say that I do not have the time to train for a full road season, nor do I patience to sit in and wait till the end to go hard. I’d agree with your points concerning MTB races. Cross is a great meathead sport. Get out there, go hard at the start, and try and rail for the duration of your race. Plus you can throw down on the weekend at your local cross race, and commute on the bike M-F. Sounds like a cross bike would be the perfect investment for you.
Check out Kona, Surly, Lemond, for good basic no-nonsense cross bikes. Test ride lots of bikes.