I bought my first six-string bass this summer after playing four-string basses exclusively for over 15 years. Honestly, I can't imagine going back to four (Ok, I could probably do with a five). Having the extended range of the B and, although to a lower degree, the C strings without losing what makes a four a four seems like a no brainer.
Why haven't you made the change to a six or even five string bass already?
'I'm 71 and still getting over the trauma from getting a 5 string at age 65…
Seriously, I play guitar and finger pick well so a switch to a 6er would not be an issue other than polishing muting technique. Truth be told, I don't play the type of music where a 6 string bass would be that useful. Then there is the cost..
But, I will say I have heard some beautiful art from masters playing a string, kind of a classical style, that blew me away.