I think there is a really important, deep principle in the idea that "they have their reward" that gets overlooked completely in many cases. Jesus never said it's bad to do good things for the wrong reasons - and that, in and of itself, gets butchered too often in church talks. What he actually said simply is that those who do things for inferior reasons "have their reward".
If they want praise and public recognition for their financial sharing, they donate money in a way that will give it to them. "They have their reward." If they want financial blessings for paying tithing, they (sometimes) get it - one way or another. "They have their reward." If they pay tithing to hold a temple recommend so they can serve in a particular calling and be seen as righteous by others, they get it. "They have their reward."
They just don't have God's reward - or, at least, not His ultimate reward - if they haven't been changed in the process to BE that reward.