Buying: might help with game balance if buying attributes worked more on a bell curve like in GURPS. An increase to 11 or 12 cost 1, and increase to 13 or 14 cost 2, 15 or 16 3, etc.  This makes the cost of having higher attributes much more expensive.

Losing: some monsters upon successful hits or spells should be able to zap attributes.  Remember the Balrog in LOTR? When we played D&D years ago our GM had you lost attributes whenever that thing hit you with it's whips. Made you run in fear from one unless you really had to fight it!