At level 30 you may want a party of 4-5. Definitely not soloable/duoable at that level. The journal explanation provides an accurate analysis of how many people you may want at that level.
Update: Duo'd the lvl 30 paladin quest with a Gladiator / Conjurer, both lvl 34. Not too difficult, other than we didn't know which targets to kill in which order, and killing the lancer first would've been better. No deaths, but one very close call.
We'll probably group for the 35+ quests. Related to that, we're on Hyperion and could use a friendly linkshell if anyone is interested. :D Edited, Apr 8th 2012 10:29pm by StasisKorial