I personally would wear the same helmet. If you end up riding a ton, maybe spend money on something more. Its mostly synthetic materials and styrofoam anyway. I can see getting a new one if you drop it or something, but practically speaking its a bunch of styrofoam around your head, which biodegrades in like 5000 years.
A lot of people in a lot of states that allow it ride with no helmet at all. However old your helmet, its about 10,000x better than that option.