I see no reason not to gather these up just like we've been doing with weapons. If people would like to pitch in on this effort, that'd be fantastic.
All sprites used to gather these values should be at least level 75 and have the damage attribute of their skill maxed, much like how fully heated weapons are used for the wiki values. If you have a lower * sprite and would still like to contribute, go ahead and do so. I would certainly like to crunch those numbers somewhere down the line.
All the values I know of are currently found at in this spreadsheet. Ray of Light is not included because it deals the same damage as Flame Barrier, so values submitted for RoL will go there. Haunted Haze and Violent Heart Attack are also not included since they are bugged.
When all the values for a skill has been gathered, I'll put it on the wiki in a damage table on the sprites respective pages.
Of note, Maskeraith's Caustic Quills are very hard to gather numbers for due to its high chance to poison, and the poison lasting longer than the quills themselves. For this reason, try to find poison-themed enemies to test these values on.
Recorded here.
I also labeled in the chart what the skills were at (fully upped firebolt, only cooldown for flame barrior). I'll probably take the data again when it reaches 4*. I'm interested to see the rest of the other 5* values, but unfortunately only have a maxed Seraphynx.
Edit:
Dunno if anyone is ever going to pick this up again, but I just added the GH values for a lvl 100 drakon's 2nd and 3rd skills with varying skillpoints for damage as a new sheet in the link above.