Started fighting them with my necro at lvl 16, stayed until i dinged 20, did the same with my wizard and now my druid is here and he is lvl 19 going to level him to 20, then i think it will be to slow, at 19 i think like 70% are still blue rest lightblue.
If you go here with a warrior and a healer you can fight almost constantly, usually this place is empty so no competition for the spawns, loot is not bad, many dropped gold last time i was here and i got 2 runes, 5 words and 1 chanter page and some 100 gold and over 1000 copper :)
this was during my lvl 19 - 20 wizard run.