The 3rd one you linked is actually not that bad imo, but I actually struggled with the same ones you linked. Here is what I found.:

1. Lower City: I didn't even try when I 1st hit 70, seemed too far away. I bought the healer helm which needed keepers of time rep. It is actually pretty close to the caster one in terms of
helpful stats, & just replaced it with S1 a few days later.

2. Shatar: happens to be linked to Scryer/Aldor Rep. Take advantage of that synergy & raise whichever you need before you even try the instances.

3. Keepers of time: This is the easiest of the 3 you linked to raise. Completion of the 2 event quests is almost enough by itself.

Regarding your question about the Durnhold event, Did you get the bomb things from the guy at the entrance, Set the buildings on fire, & kill the 1st boss?