Quests are fine as is, I think. Somewhat hidden so you get to do some discovery. I really enjoy that part of it and wouldn't change it.
Overall though, compared to most other online type games, PVE in Achaea is terrible. It reminds me of using only auto-attack to level up in something like WOW, EQ, or others, take your pick. Battlerage has added a few skills to it, which is nice, but at the heart of it, all it did was add a bit of coding work to optimize battlerage handling.
I propose one of the following:
Completely overhaul PVE - I expect this to be less of a possibility because of the amount of rewrite required to something core and already in place. Alternatively (and more likely), create new areas with a completely different architecture for PVE.
You could do things like Tank, Puller, Healer, DPS, CC, Debuffer, Buffer as archetypes, a standard that so many online fantasy games have been successful with.
These new areas could be instanced (or not), and your new PVE skills could only be used in these areas (to keep them from messing with combat or current bashing balances).
PVE Raids could be done on castles, dungeons, dragons, or what have you, with real world consequences. For example, the most recent winners of said raid could get a 24hr experience boost, or gold boost, or favored or whatever. Lots of ideas to be had here, the community can come up with more than I can for sure.
The content could scale based on the size of your party, but making the skills of each "subclass" with sufficient potency to impact the overall fight.
These archetypes could be added as a "Subclass" that anyone could purchase, but you couldn't have more than one or two (and only one active at a time). Or each current class could have it's abilities defined for each. (Shaman would be a debuffer, DSL knights DPS, SnB knights tanks, etc).
New artefacts could be introduced that increase/decrease the agro you generate, that hold up a single denizen (like additional CC), that increase healing in only these areas. Artefacts that break you from CC, reduce the damage dealt by said denizens, add an additional subclass, reduce time to change subclasses, and a plethora of other options that all relate to this new PVE content. I bring this up because any large change or implementation such as this should have some sort of ROI for IRE.
There are many considerations here too, overall experience and gold gain must be balanced and on par with the time spent today. I'm not looking for a quicker dragon, but for an enjoyable and challenging PVE experience. Achaean combat has a depth unparalleled by other games, but not everyone wants to be a combatant.
This would be, as far as I know, the first MUD to have something dynamic (for PVE) like this and in my opinion, take great strides towards hooking new mudders. Any new mudder today has most likely played one of the recent day online games at some point or another, and by comparision, the PVE in IRE games is dull.