Depends on how you count worth. The lawyer who volunteers at a soup kitchen, to use a lesswrong.com example, is giving up X dollars per hour of income to provide far less than X dollars per hour of charity, and since this is true for people who give to charity in general (without reference, but I'd be very surprised if it were controversial), it seems clear that people who primarily give time are donating for reputation rather than effect. I've no clue about the relative proportions of time and money the religious and non-religious give, though.