On the contrary, I think hours as valuable consideration is vital to include in the compensation list. It is something you'd otherwise have to pay for - ergo getting it for free is payment.
I also think common purpose is an excellent open-ended criterion that can be used if necessary to nab illegal charters. Best left undefined like 'conjested area' for flexibility whan needed.
And finally, equal cost share. Utterly essential to combat the blatant abuse of the system by Wingly.