I've played 4ers for more than 10 years. I hated 5ers. I play metal (exclusively). So at some point that low B became a necessity - but I fought against it all the way (after so much time on 4ers that extra string felt weird and confused me a bit, heh). Fast-forward 2 years: the transition from 4ers to 5ers was complete. Now I have 6 basses - all 5ers. There was no point going back once I've finally adjusted to the dimensions of a 5 strings neck. On the other hand I'm playing only Ibbys SR and that helps a lot 'cause the neck is still very slim (for a 5er).
So regarding your question: it depends on what type of music you play (whether you stick to one genre or not), how fast you can adapt to new things & your playing style. Ppl have managed to play ajust about anything on 4 strings for decades. You don't have to get a 5er, but playing one opens a lot of possibilities. If you do decide to make this step, give it time. You might feel at home using a 5er or you may initially hate it (as I did) - just let it sit and try cope with it for a while before making the final decision (stick to 4ers or go 5ers ... or more)
Have fun 
So regarding your question: it depends on what type of music you play (whether you stick to one genre or not), how fast you can adapt to new things & your playing style. Ppl have managed to play ajust about anything on 4 strings for decades. You don't have to get a 5er, but playing one opens a lot of possibilities. If you do decide to make this step, give it time. You might feel at home using a 5er or you may initially hate it (as I did) - just let it sit and try cope with it for a while before making the final decision (stick to 4ers or go 5ers ... or more)
