Like Jazzyvee, I've only used the separate stereo outputs on rare occasions in my 40+ years (!!) of playing Series instruments. As you've discovered Michael, it is a wonderful huge and open sound to have separate amps for each pickup, but it's not always practical. Jazzyvee mentions a gig where the PA mixer was willing to experiment and used 4 input channels just for bass. That's a rare situation for sure. Plus, you are then counting on that engineer to balance your sound for you and they may have a different idea about it...
When I had a stereo amp rig about 100 years ago

it included a stereo chorus whose input came from the bridge pickup only but whose stereo (100% effect only) output was then blended into both amp inputs. When kicked in the overall tone got brighter and started rotating around while the fundimental from the neck pickup was unaffected. It was a wonderful sound! The rig also had a summing network which would corral all of those signals back to mono, through a DI to be sent to the PA.
I also used stereo mode on a few rare recordings, panning the two channels only slightly left and right. This was enough to open and enlarge the sound slightly but still appear to be centered mono bass.
Again, there are no rules about this stuff so keep experimenting. But to answer your question directly; I now always run my basses in mono.
Jimmy J