Yeah serve fests are SO captivating
If you really want tennis to nosedive in the ratings, speed up the courts to the max. Good idea
Then R.I.P. tennis as a source of entertainment.
The only way to go is medium paced for most events (players can use all their weapons: offense and defense) + keep some extreme slow and fast to spice things up and for some good old fashioned contrast.
About doping issues, chances are they all do stuff to improve their perfs, endurance, speed and so on. Pro sport and idealism tend to not mix well especially when a huge amount of money is at stake. For the most naive among us: welcome to the dark side of human nature.