There might be, but yeah, that's not the main reason for searching IMO.
See http://primes.utm.edu/notes/faq/why.html, but it boils down to "something really interesting can be found along the way, primes relate to other important topics so learning about them has intrinsic value, there's some money in it (but you have a 99.9% chance of spending more than the prizes in your search... and you still won't win)".