Roller rockers have the most advantage over standard rockers when valve spring pressure is really high. At lower spring pressures, a lot of the advantages of roller rockers disappears. Those benefits include stiffer structure, less friction (lower oil temp) and more accurate rocker ratio. The stiffness isn't as important at lower spring pressure, and lower pressure also reduces the friction of the standard parts. The only important difference is the accurate ratio (and the gee-whiz factor, of course.)
At .500 lift, and assuming your springs are reasonably matched to the cam, I don't think you're in NEED of roller rockers, but they certainly won't hurt anything except your wallet. If you have enough disposable cash, go ahead. Don't expect to magically find another 20 horsies, though.
Be sure to verify your pushrod length when you're done. I've seen enough roller rockers with non-stock geometry that requires different length pushrods.
