Thatch after her most recent rebuild.
I ride 3 bikes – a commuter for every day use, a touring bike and a road racer. Each are special in their own way and, each are well equipped and maintained. In the warmer, dryer months, I cycle most days averaging 200-300 km each week. And, I ride each bike most weeks.
When I commute to the office, a few days a week these days, I normally ride the commuter, a 20 year old retro fitted mountain bike setup for road cycling. The touring bike is equipped with a 10-speed Ultegra compact drive train and Shimano trainer wheels. And, the carbon road racer is setup with all Dura-Ace components and wheel set. I save these bikes for weekend rides and cycling events.
There are 3 key benefits to riding several bikes.
- Less wear and tear. No 1 bike is ridden all the time. The wear and tear on the bikes is spread over 3 instead of 1. This is particularly important if you put in a lot of mileage and ride in the wet weather.
- More frequent cycling. I ride in all weather conditions. The commuter is fine in the wet weather but I would not consider taking the carbon bike out in those conditions. I can also ride the commuter on trails that are not suitable for the road bikes. This gives me more routes to chose from and adds interest to the rides.
- Improved training. The commuter is heavy. It takes more effort to get it rolling and, in particular, climb. I ride the same training routes on this bike as I do on the road bikes. It’s harder but develops power and improves my pedalling technique. When I get on the carbon bike, it feels like a feather and almost climbs by itself.
PedalWORKS 
The rules: the correct number of bikes is n+1, where n is the number of bikes you currently have.
So you need at least one more. Folder, mtb?
Although I actually use almost exactly the same combination as you and the old MTB frame set up for road does more miles than any other.
LOL! N plus 1.
I also have a cross country mountain bike but it doesn’t see much action. I have go somewhere to find trails.
I’m jealous… I would like a steel frame bike for commuting and long comfy rides, as well as my road racer, and a fold-up bike just to be handy, and eventually a tri bike as well. Sadly with two of us who love bikes in our tiny flat, and not enough room really for even two bikes, the dream will have to wait!
Be patient. It has taken me 30 years to accumulate the bikes.