Ad Frequency capping can be an extremely powerful tool to manage and improve your CTR and average CPC. It is also often ignored very much.
Adwords provides data around Frequency and Reach. This can be accessed by logging into the Google AdWords panel and using the dimensions tab.
Both of the above are intuitive & expected. Consistent exposure to the same creative should obviously reduce the overall response rates.
Two basic optimizations can help improve CPCs –