The fluted ones are marginally lighter, but the real advantage is a smaller surface area for friction with the spring. I guess if sand or grit gets in there the grooves would allow it to be pushed aside easier too.
I'm no expert but the only other upgrade that I would do out-of-the-box is a USGI rear sight.
That having been said, the flat op-rod spring guides are perfectly functional and a lot of people seem to be having better luck with Norc rear sights lately. I'd shoot it a bit and see how it does before breaking out the credit card.