I've had my 6er about a year now. I haven't touched another bass since I've had it.
I prefer the tighter spacing. The neck is actually really slim. It's improved my playing a lot because the next note is always under my fingers without having to do fretboard gymnastics. It's improved my technique, because it really forces me to work on muting, while a 4 string is a lot more forgiving. I love the fatter sound and the feel of playing what would be the low notes on the E, higher up the neck on the B. So for me it does everything a 4 or 5 does, and more. Plus to me it just looks much nicer. I've ever been a fan of traditional "Fender" shaped basses. They've always struck me as being just a little dull. And a 4 string just looks ridiculously skinny to me now.
Of course this is all personal preference and extremely subjective. But in answer to the original question, yes for me playing a 6 was extremely addictive. I went from having never even played anything other than a basic 4 string, to not playing, or having any desire to play anything other than a 6. I can't see myself ever going back to playing a 4.