Do We Need Incentives?

My son is trying to cut 3 seconds from his breaststroke time. 3 measly seconds. When he finished the race, one of the parents said, "Do you have an Xbox? What if your mom bought you an Xbox if you cut those 3 seconds?" We have an Xbox.  I looked at the man, who is sort of a family friend and said, "He wants to do his best because he wants to do his best, not to please his mom or get a present." The man said," Oh, ok"  Then I said hopefully to my son, "Right?" He nodded. I thought about this the rest of the swim meet. At dinner, we have debates on this topic. My oldest son insisting that more would get more done and done more efficiently from everyone if I would just offer a financial incentive. He proves the point because if someone wants extra money to do something and I throw in 5 bucks the floor almost always looks better. But I do not want that!  I want my kids to do their best all the time because it is right to always do your best, not because they will get money. The son reiterates his position with the paycheck argument. He formed his conclusions from personal experience. He would be in charge of babysitting his 4 younger brothers. Not easy. As part of getting paid for babysitting he also had to keep the kitchen and rest of the house clean. Not easy. My husband and I would come home from our date nights and the children would be asleep, the house tidy, the counters clean and shoes lined up neatly. My son managed this by bribing his younger siblings with a magic "prize box". He would spend maybe a $2 grand total at the Dollar store and put little plastic junk toys inside an empty shoe box and tell the brothers if they cleaned and went to bed they could pick whatever they wanted from the prize box. Whatever they wanted they could pick! And even though a 4 year old was able to realize and comprehend he was getting only junk for all his effort he still consistently put forth the effort to get the prize. When they ask me now if they could get money for doing something I tell them their reward will be heaven.  My oldest son still insists I could say heaven all I want but by offering a concrete prize the effort and result will always be better.  What do you think?