Depending on your work / type of trips you do:

1. If you need to rent a car often make sure you have a status card and use one of the major companies. Points and upgrades are nice but the time saving of just walking to you car can be huge at places.

2. Same for hotels, anything that allows you to check in online and not having to wait inline makes a difference. Especially if changing hotels daily.

3. This depends a lot on the type of person you are / company you work / your contract / etc but I would say in general that road warriors in many occasions get taken advantage off. Yes you get to fly away, stay in hotels etc but overall the amount of work vs compensation is lacking.