1) Soften XP penalties based on the race/class/popularity/power of a particular combo. The goal here is to give such a combo a more sensible level range to deal with. For example, a human ranger has an XP penalty of 200. An elf ranger's is 700. Considering that there really is no great advantage to being an elf ranger...in fact, I think most might agree that the elf is disadvantaged compared to the human, the current system really sort of screws the elf, right? I don't think every single instance of this needs to be re-tooled, but some of the ones that spring to mind are dark-elf necro, felar AP, cloud healer, and gnome warrior (shoosh I don't wanna hear it!).

2) I posted down below as a reply, but I'll post again here - make movement regen much better for all levels (not just the low ones), but make it so that it goes back to how it is now when adrenalin from a PC encounter sets in. This makes it so that mv-hampering tactics are still viable in PK, but there would be less down-time in the midst of action.

3) How about making the whole Area Explore concept scalable based on your level? For instance, any character at level 51 won't be too freaked out by gathering a group and exploring the castle of barovia. But, take a group of three level 25's and it is a pretty epic proposition. The net result would be increased explore and observation XP for those who tackle relatively difficult places earlier in life. Additionally, they'd gain the benefit of a swift corpse decay and gear return. I'm sure tons of other cool ideas could spawn from this. Also, if you die in an area explore, how about reducing or altogether nullifying the XP penalty? I mean, you're taking a chance by even going to one, because they are inherently more difficult than standard areas. Ideally, the new Explore-For-Tots areas would be chock full of questy goodness and cool gear, so it might mean a long-term retrofitting of some current places to live up to that.

Edited to add: One real pain in the butt for non-high-level characters to deal with are nasty maledictions that last for exceptionally lengthy amounts of time. I.e.; PLAGUE. The fact of the matter is that abilities like this one make exploring a very daunting proposition for lowbies and midbies. I'd suggest revisiting some cases where mobs cast it or "skill" it like freaks. Case in point; that mummy in the castle of barovia.

4) Tiered cabal raiding and retrievals. I know, crazy right? But, check this out: What if cabal members could only raid/retrieve for whatever portions of their cabal powers that they can currently make use of? This would utterly eliminate the effectiveness of lowbie retrievals, and even raids. Each cabal could be made quite a bit larger, with various guardians instead of just an outer and an inner. Each would basically hold sway over a given power. So, let's say the nightwalker at the Chasm guards over divination and nightfist, but if the Scions are holding an item, it guards the lowest tier powers of another cabal. So, if the Scions had the Orb, lowbie squires and acolytes could kill the nightwalker to regain zeal and golden aura (or whatever the hell that power is called). I'm not necessarily saying this is a great idea, or that this would be the best way to implement it, but if the basic gist is followed it could result in non-hero ranks being just as exciting from a risk/reward standpoint.