This is a very subjective question with parameters that should not be ignored. If wagering on a driver who is listed at relatively low odds (approx. 8-1) then you clearly would not want to bet on more than a few drivers to win the race, as it could deeply cut into potential profits. This becomes more profound if the driver with the lowest odds wins the race, or worse yet the winner is not bet on at all.
On the other hand, if you are looking to structure a wagering ticket that is made up of several mid range or long shots drivers at 15-1 or higher, then you have the ability to take more chances. In this case should your driver win then you would still have an outstanding payday at the betting window. However, with this strategy, it is considerably more difficult to get a driver with long odds into Victory Lane.
If the race is scheduled to be run at a track like Daytona or Talladega then nearly any driver in the field has a chance to win. In cases like this, it makes sense to sometimes take an informed shot on several drivers at higher odds. This is partly due to the type of racing produced at these tracks which usually involves many wrecked race cars. Often there can be strength in numbers in these situations, and having a team of drivers can sometimes be a wise approach in attempting to earn a profit.
There are some tracks and circumstances where the approach should be in the opposite direction. In some situations, the best option is to maybe only bet one or two drivers to win a given race, or even perhaps none at all. An example of this would be watching the weekend progression and seeing that one car and driver is really dominating over the field. Typically when this happens the oddsmakers will react swiftly and lower the price on the dominating driver to win.
Wagering on a driver who looks outstanding going into a race is usually a dangerous strategy because so often the best car in practice is not the winning car of the race. The lowered odds make it even more risky. Worse is having the race play out exactly as handicapped and the driver who you are supporting has a problem like mechanical issues, on-track incidents, and unforced violations. These are all issues that do come up, and for those reasons alone it makes wagering on heavy race favorites very volatile, and typically not advised.