yes, either your traffic will increase or decrease. In terms of rankings, it may lower your rank, or simply put your newly rewritten URL in supplemental index.
if you will change url and you think it's worthy enough and will benefit you more than your previous url then do it, and just don't forget quality link building!
Another beginning for your site but if you think it will benefit your site do it. But if you getting quality traffic to your current URL don't change it try to improve it.