Sorry for not replying sooner -- I was out getting beaten up by a golf course, leading once again to the question, "Why do I play this stupid game."
Groove sharpeners don't make any difference unless you consider their groove cleaning function. But there are cheaper ways out there to clean your grooves.
As odd as this sounds, grooves do not put spin on the ball, so whether they are sharp, dull, or non-existent does not matter. Ralph Maltby, Tom Wishon, Cochran and Stobbs, and SMT guy (sorry, can't remember his name) have all stated this. (If you go to GolfWrx there are long discussion about this.) I'm sure there are others, but these are the only ones that I have read myself. Theodore Jorgensen doesn't discuss this specifically in his book The Physics of Golf, but his explanation of spin only refers to the compression of the ball and friction against the club face and makes no reference to grooves. Ralph Maltby actually proved this theory by designing and playing a grooveless set of irons.
The function of grooves, according to these sources, is to channel water and dirt/grass away so they do not interfere with the contact between the ball and the club face. Reduced contact would reduce friction and, therefore, spin. The USGA proved this by doing testing with clubs with and without grooves in both wet and dry conditions. Spin rates with grooveless clubs were the same as those with grooves under dry conditions, but were considerably lower in wet conditions.
So, as I asked Tom Wishon, why do grooves "wear out" resulting in reduced spin, as is shown in videos produced by some wedge manufacturers. His explanation is that (I'm paraphrasing) the face of club is not perfectly flat, but rather has very small ridges that do increase friction/spin. Over time, the force of hitting the ball flattens these small ridges, which reduces the friction.
I have yet to find an answer to the question why the USGA changed the groove rule if this is the case, but I haven't got an answer to that one.