The very reason why Blizzard introduced the concept of Nephalem Valor was to incentivize players to stick to their build; before NV existed, people were running around constantly switching skills, because "everybody else was doing it," creating a feeling of "If I can't be bothered switching skills evey 30 seconds (or simply like to stick to one particular build), I'm at a disadvantage." It's the exact same deal as using your second weapon slot in Diablo 2 to cast Ice Armor / Clay Golem / what have you. Blizzard felt this was a stupid/wrong way to play the game, so they introduced Nephalem Valor to counteract that metagame shift and give us a reason to flesh out versatile character builds that can cope with different situations.
Many people have complained about the absence of skill points in D3 (-> "OMGZORZ EVERY1 HAS SAME SKILLZ!!!). If everyone were to switch skills freely on the fly, this statement would actually be correct in a sense. Nephalem Valor, on the other hand, encourages us to make our own, semi-permanent decisions on character builds.
The fix to this "problem" is pretty retarded.
There is already a good incentive not to change your skills every 30 seconds, which is that changing your skills back and forth every 30 seconds is a pain in the !@#, especially if the skill has a long cd.
It's also not necessary to change your skills every 30 seconds. I haven't even played this game since the summer, cuz there's been no PvP, but back then, the only time I would ever want to switch my skills up, is when I was fighting a boss. Obviously, my AOE setup is not going to cut it when I get to a boss, especially when my items suck.
Changes are only needed the odd time, when you encounter something rare. The whole NV thing kills build diversity, and build exploration, while screwing over poor players who don't have items that are good enough so that an AOE setup can kill bosses, or a single target can take down large groups quickly, or that some "compromise" between aoe/single target is actually efficient for both large packs and single targets.