Lets run some numbers on RG, assuming a full artifact tree with no relics.
A non crit RG will heal for 214.8 * 1.1 (blessing of the world tree)=236.28% SP.
A crit RG will heal fo 214.8 * 2 (crit modifier) * 1.8 (living seed + seeds of the world tree) * 1.1 = 850.608% SP
This ignores the rather minimal hot portion of RG, which mostly contributes to mastery.
A crit RG is therefor 3.6 as strong as a non-crit one.
Assuming 15% baseline crit (not sure if this is a reasonable number), RG without abundance would average to 697.026% SP, whereas with abundance this naturally goes up to 850.608, or 22% boost. This gets better the lower your base crit is, assuming abundance caps it to 100% regardless. For example with 10% base crit the boost is 27%.
Lets compare this to Healing Surge. They both cost practically the same.
A non crit HS will heal for 450 * 1.06 (grace of the sea) * 1.15 (buffeting waves) = 548.55 SP
A crit HS will heal for twice that, or 1097.1 SP.
The crit % of HS is somewhat tricky to compute, as it depends on the uptime of Tidal Waves as well as talent choices. I'll assume tidal waves for every 3rd HS, then without crashing waves the average HS will have +20% to its crit modifier. Assuming 15% base crit, this puts the average HS at 740.54% SP.
This puts RG and HS at the same ballpark, although it doesn't factor in mastery.
Lets go back to druids. Disregarding mana costs, the HPCT of CW and an RG with abundance vary by 200% SP. 1 CW and 1 non-abundance
RG are 50% ahead of 2 RG with abundance. Therefore, ignoring hot duration extensions, abundance overtakes CW once you cast more than two RG in a 30 second window - which is of course going to happen in a dungeon.
Lets assume we flourish on the CD and it always catches CW, and furthermore assume we use CW on CD (the latter is highly unlikely as it will increase CW overhealing). To overcome the free CW (GCD wise; assuming the non-CW build also flourishes at the same times), would take 10 RG casts per minute - again, a reasonable number for dungeons. This is measured by 2 RG taking the place of the 2 CW, and the other 8 RG being stronger.
Finally, CW also boost mastery. With 30% uptime (assuming flourish) on a target with multiple hots already (the tank, which will nearly always be the target of CW), the effect is rather marginal.
Now, if you toss in the legendary wrists -
http://legion.wowhead.com/item=13709...aya&bonus=1811 - things change.
I also wanted to compare HT and RG under abundance. Lets assume 4 RJ targets which puts HT at the GCD.
A non crit HT heals for 360 * 1.1 = 396% SP. A crit one would heal for 1425.6% SP.
With 15% crit chance, this puts HT at 550.44% SP. The HPM of HT in this case is 1.3 times better than RG, which means that at least numbers wise, it is worth casting for periods of low damage, but the healing is very swingy. At 0% crit it has slightly less HPM than RG, for example.