I was in a similar boat. I played a 4 string for about 40 years. The reason I purchased a 5 string is in the form of a question.
How often does a singer ask you to transpose the key of a song upward? I my case, pretty much never. However, they frequently ask for the song to be brought down a key or two.
So...when you do that enough, you start realizing that your losing the sound (closer to the correct octave) of the original lick.
Going to a 5 string with the low B allowed me to keep the original intent of how the bass line was suppose to sound.
I thought that I would only use it on the songs that I needed, but being the lazy bastard that I am, I got tired of switching basses in between songs.
Further more, after a couple weeks of mind torture (you mean that bottom string isn't my E) I got proficient at it.
Now, I totally prefer the 5 string.