I played a 5-string bass pretty exclusively for several years of gigging playing in a hard rock kind of jam band and thought I would never go back to playing 4 strings until just recently when I began playing more indy rock style music. I still switch back to the 5 occasionally, but I rarely have a need to go deeper than a low E.
I guess I would say now that I prefer the feel and simplicity of a 4 string bass. It's a classic tried and true. However, when I have to play those low notes below E, usually because I'm playing with a vocalist who is picky about singing in certain keys, I REFUSE to detune my 4th string (just a pet peeve of mine). I would rather have my 5 string on stage to make a quick switch for any song that I need lower tuning for.
Both my 4 and 5 string basses are Fender Jazz's fitted with Leo Quan Badass bridges, so string spacing is probably on the narrower end, although there's no noticeable spacing difference between the 4 and 5. Of course, the 5 string has a much thicker neck, but it's something I think everyone can get used to over time.
The great thing about having that extra fifth string is that although it gets less use than the others, it provides me with the perfect thumb rest while I'm finger-picking the higher strings. I miss that when I'm playing my 4.
One complaint I have about my low B is that on a regular 34" scale bass, the tension is a little loose, causing some rattling and a generally "floppy" sound when striking the open note. Some players say you need a longer scale bass if you're gonna go 5 string so that the tension is higher, but personally, I can't physically play those comfortably because of the increased width between the frets but that's just me.
Cliff notes: 5 string basses are sweet and I think any player can benefit from having at least one in his/her fleet.