It sounds to me like you want something that is fun to ride locally on gentle trails and roads, OK for commuting but also robust enough to deal with some occasional tougher offroad routes.
Not a very STW response but in your position I’d just buy an extra set of wheels for your 29er with cross or road tyres fitted.
Or if you want a change, as above something like a Fargo would be a good call. Or perhaps a Swift?
If I was to keep one bike it would be my Surly Karate Monkey – versatile as hell, can be run geared or singlespeed, takes racks and guards, tough as old boots and really capable on properly rough stuff but also quite happy run with drops and slicks for the road.