It's cheaper to buy new ones and shard the old ones, and everyone knows xur loves sunbreakers so it'll only be a matter of time before they make an appearance again. But since hard raid will be the only way to get a legendary helmet that will get you to 32, you'd probably be better off reserving your exotic spot for a helm. But if you don't care about lvl or light and raiding and all that jazz, then go for it!