Let me share with you the XP system we devised for our group. It is fairly simplistic, but it does not necessarily match the reality of playing.
In our campaign it takes 10 points to make a level. (we play once per month)
1 point for: showing up and being ready to play on time (*** since we play Sat AM, we did this to encourage early arrivals)
1 point for: actively playing in the session (no sleeping on the couch and having us to wake you up to roll you combat dice and you have to attend at least half the scheduled session to get it)
1 point for: actively RPing your character in the session
That means that everyone can make 3 points for showing up, participating and RPing. On a Saturday AM being hung over can be bad for your characters XP.
In addition to those fixed points, there is a bonus point for each session. This bonus point is split up into two parts. We do a secret ballot at the end of each session where people vote on who they thought was the BEST RPer and the BEST game players (i.e. cool tactics, etc). The winner of each of those votes gets 1/2 XP. So if you win both, you get a full bonus point. When voting, you are supposed to be a short note on WHY you voted for them.
We also have the ability for a DM to hand out bonus points at their discretionary if the party did something momentous. (bonus XP for finishing the adventure arc, etc).
Since we require 10 points to make a level you will get a level about every 3 sessions. No matter what the adventure entailed. If you spend most of the session in town RPing, finding information in the library, etc... and had a fight or two... you still get the same XP as a dungeon crawl. This was done by us for several reason:
1. Promote RP: We are there to enjoy ourselves. Human nature wants to improve on character so it provide a steady growth to the characters.
2. Missed Sessions: If you miss the dungeon crawl session, you would miss all the XP from it. This levels it out to keep the characters near the same levels.
3. Got rid of annoying XP charts.
4. Keeps all the characters who attend in the same level range... you have to miss quite a few sessions to fall far behind the party.
5. Prevents going monster hunting to just get that last 200xp to get a level. You get your XP when you get it.
To be honest, the voting for best game play and RPer was the best part of the XP system. It is surprising how well that was received and the comments come with it. It has been a very positive thing for our group.
I know this probably will not make the DCC RPG as it is a far departure from other game systems, but it works for us.