I never joined any groups like this nor do I care about clearing dolmens at all. I personally don't get the attraction of doing dolmens on repeat like this... Sure, I'll clear them out if one is active near me but I don't go out of my way to do it.
I did a Dolmen exp Grind for the first time this event and have to say it's worth it (for me): EXP scroll + Even EXP bonus + Training gear. Survivability was basically a non-issue. I got 2 toons from 10-50 in two 6-hour days each. I prefer it this way because now when they do their overland quests, dungeons, bosses, etc. all equipment drops will be CP 160.
But yeah, I'm pretty sick of Dolmens, lol. Fortunately I just need gold to buy overland jewelry.
And I don't think I would do it again unless it was during another Double EXP event.