I like the wilderness areas in the game, I find them re****l. Unfortunately due to the way they work there's very little benefit to running them past a certain point because you're going to do a LOT of work for not very much XP.
So, how about instead of having a progressive slayer where each rank takes more kills and gives more XP, have a flat slayer where every, oh, 25 or 50 or 75 kills (depending on the area) gives a flat amount of xp? Maybe have repetition penalty apply to it so you get -25% for every time you get a slayer completion in a given area. This will allow people to jump in and do some slayers for xp if they feel like it and still get benefit, but will prevent them from just endlessly grinding slayers to level up (not that they'd probably do this anyway--it'd be seriously boring).
Rares still give XP on repetition, although the -67% is kind of harsh IMO. Maybe make this the same as other repetition penalties? -25% every time you do it on a given day? It'd be consistent, then. You can't get the big chunk for getting ALL the rares a second time, anyway.
For explores, you could create a mini-quest that fires off when you first enter the explore area that gives you five or six or whatever random explores to re-visit for a single chunk of xp. Which you could throw repetition penalty onto.
This would mean that explore areas don't stale out after a run or two, so if you're just bouncing around you can go churn some XP on your own no matter what's going on.
Edit: that's the most hilarious redaction I've ever seen.