Yeah, personally I like the fifth legacy emblem better and you can get the feeling of completion. As far as rewards, there aren't very many, not worth legacying over in themselves. But I wanted to legacy so I could continue to level up. That's really the only reason I think you should legacy. I'd buy as many character items as you can/want because they'll be more expensive the next time around.
Wipe that smile off your face and get your tryhard face on!!!
I mean, come on. You did it four times. Don't tell me you're backing off NOW.
It's up to you, but the further you increase your level, the less match making will be in your favor. And with the broken match making system we already have, a cool looking emblem isn't worth it.
If you play as a lone wolf, don't legacy. Being a 75 5th legacy is the worst thing that can happen to you as a lone wolf.
But if you play in a party a lot and enjoy to do everything all over again, go ahead and do it.