XP vs Milestones
In my games i have a 2 fold 'award'.
the first is for the game itself reaching Milestones. The game is a team effort and all players get points to use in various part of my system's CH...which in ture aids in the growth for the characters, as well as grwoth they have made in RP
the 2nd is per player..a small award for miles stone in game, some times off things will trigger awards as well.
from my point of view. Having a 'goal' to reach so you get more hit points, or can cast another spell, lends itsself to people pushing numbers . ( I co-DMed a game where two players were only doing the match so they could get a high level suit of armor... when the Main DM quit, i cut both players. I lean heavy to RP in my games..if you are only interested in 'numbers' play an arena game
there was a system that stevejackson was a partner with, and has since reissued in a New Editon ( i was in on the kickstarter for that)... you gained points in various ways, and you had point levels of stats, that would tell you how much you had to 'save up'.to apply those points to IQ, ST ect ect... depending on where you applied that, you opened up a chance of new talents..spells ect.
There has to be away fro the player to grow..RP is easy..your players have to have thier Characters grow through RP..by stats are important for HPs and skills and such, or you 'don't have a point'
I developed my own system, it works rather wall, and dice rolls are there, but it isn't the main focus of the game... No Min-Maxing.. no 'trying to get that next big spell'...play the game, earn your rewards.