Gemming Expertise

Given fairly low gear levels, ~472 at present, is it worth it be gemming and enchanting toward expertise hard cap?

Yes it's worth it if you can't get to that point without gemming for it. If you can get there with reforging only then you can fill the sockets with whatever you want including stamina which you can't reforge to.

And yes, you want to go all the way to the hard cap, which is 15% which is 5100 rating I believe. You'll be attacking bosses from the front and you don't want your holy power generators missing at a bad time.

It also depends what content you're gearing for. If you're gearing for 10 mans, you might skip Stamina gemming as a whole, and only gem Hit/Expertise/Haste. It doesn't really matter in what combination you gem it, as you can fix it with reforging. Be sure to take all socket bonuses, even practically useless socket bonuses like +crit, as gemming for a socket bonus is never a loss in this case.

If you're gearing for 25 man or 10 man HC, you'd want some stamina. Still, getting Hit and Expertise capped is important.