I think haste rating is under-appreciated.

It's not just that it's decreasing your cast times, but it's as much (or more) the reduction of the GCD. How many times have you started casting a spell and wanted to interrupt and earth shock that heal?

I actually don't have any pvp experience with shaman (yet) at high levels, but on my mage, spell haste is huge. Even having a .1s advantage on that other mage when you're trying to poly each other is really a lot bigger than it would seem.

The one thing I will say that tends to support your position is that it's an expensive stat, so it takes a fair amount of work to get a serious amount of haste, and it's not always clear what those tradeoffs mean.

Anyway, not saying it's the best stat or anything, just saying that you might be surprised how much it matters in those clutch situations.