Peltiers transfers heat at the cost of power. You still need a large heatsink to dissispate the heat from the motor and heat generated by the peltier element (7.2V X 2A = 14.4W in addition to the motor). The current draw of the peltier will reduce you battery voltage which will directly affect your car's punch and speed. You will also have to deal with the extra weight of a healthy heat sink. If the heat sink is insufficient the peltier device could destroy itself.
The better way to use a peltier is to use one to cool your motor to icy temperatures before the race. If your motor starts cooler it will finish cooler. Plus you won't have any drain on your battery or have additional weight in the car. Team Much More has a peltier based cooler to use on the motor before the race. At $100 price point you can build one using a peltier element, CPU heatsink/fan, and copper piping for much less. Good luck.
Team Kyosho, Orion, KO Propo America, Avid RC