Jackstraw: All my colleagues have told you the same thing, more or less. The entire amount paid in any transaction goes to the seller's agency. They usually have, in a contract with the seller, agreed to split the commission with the buyer's agency. All funds, except reimbursement for out of pocket costs that the individual agent can present (such as paying the Home Inspector on the spot) are put into checks made payable to the agencies involved. No checks for general disbursement are made to the agent. Therefore, the agency completely controls where the money goes. Most agencies take the total amount and split it as per the agreement that they have with the agent. Some will allow a pass though of the bonus but, as I understand it, this is not the usual case.
As my colleagues have told you any agent has good enough motivation to show listed properties that carry a full commission and that, therefore, adding to the pot does little good. Finally, unless the agent can practice some form of mind control, the buyer makes his own decision. If it were not so, wouldn't the agent only show one house, that where his revenue was the highest, call it a day and have his buyer sign on the dotted line?
My own opinion is that what you should do is price the house appropriately and if you feel that there is some money left over for promotion, either add it to a closing cost bonus to the buyer or do some improvement that will be eye catching, since the average buyer makes a decision in fewer than twenty minutes. (Although they may well spend more time thinking about it after leaving the first showing.) They rarely come back a second time without being very interested in the place.