Well, Lava Burst does not benefit from haste or crit, unless you cast it without a Flame Shock on the mob; the cooldown is fixed and it should auto-crit.
Flame Shock is an instant cast and a dot, so the initial hit can crit but haste does not help it either.

Our other shocks gain nothing from haste, but crit can help them a bit.

Lightning should be about half our damage. These spells benefit from both crit and haste, although certain percentages of haste are bad to be in, due to our optimal dps rotation.
Binkenstein has worked out ranges of haste to avoid (note, in a raid haste is not consistent, drums - bloodlust/heroism and other effects can change it):

18.75% - 20.20%
25.00% - 26.45%
37.55% - 39.00%
43.75% - 44.90%

As far as our spell arsenal, our priority should be hit (#1), spell power (#2), then we no longer have anything which helps all our spells.
I'd personally value crit over haste, but there's a lot more haste gear out there.
If your haste gear with typical (raid) buffs does not put you in the above ranges, haste is good. If it does put you in those ranges, you're better off banking the piece then wearing it, until you get enough other pieces to not be in those haste ranges.
As far as item points go and item points per item level, Hit > Spell Power > Crit > Haste.
As in, if an item level 50 had one stat on it and nothing else, all hit would be a bigger benefit then all crit on one piece at the same item level.
So if your gear is from heroics, and your best choices are 20 hit rating or 20 crit rating, the hit rating will increase your dps more (until hit capped), etc.