I switched to five-strings in the late 80's and never looked back. I'd not owned a four-string bass until I bought one on a whim a few years ago, but, it's NOT the start of a trend . . . . .
For me, I got tired of shifting constantly on a four, starting a little lick or figure HERE and then having to jump or slide up to THERE to finish the thought. With a five, I could play two full octaves across the fingerboard, and it all suddenly made a lot more sense.
I'd begun to run into situations where I could really use a low E-flat or D, but I just wasn't smart enough to de-tune for this song, then tune back up for the next, just too much monkey motion.
I always say to think of a five as a separate and different instrument than a four. It mutes differently, the fingerboard/neck can be a lot wider/bigger, you have similar but expanded fingering directions to go in, it's just a different animal than a four-string, at least to me.
I can absolutely tell you that buying one just to pick up a few extra low notes as the only reason is a total waste. On the other hand, if you can embrace the difference and it works for you, transposing to E-flat, D, whatever is effortless and to me well worth it: It's just easier if you have to spend a lot of time where this could be an advantage.
I would never go back full-time to a four, it's just not me. Each of us has to find that spot that works for us, and going from a four to a five may . . . . . or may not be for you.