The short answer is – it depends. One thing is for sure, mailing out one piece of mail to 3,000 people is far less effective than mailing out three waves of mail to 1,000 people. You may even need far more than 3 waves per person depending on a number of factors, such as complexity of your offer. Test and measure each wave to learn what your response rate for each, then calculate your ROI to determine how much profit you made from each wave and your overall program.
Using a unique code for their responses will help you determine which wave sold your prospects. If the third wave is the most effective (and is profitable) try another wave and continue to do so until your response rate goes down. Also, it is not necessary to change the mailer every time. Sometimes sending the same mailer multiple times produces better results than changing the mailer. The key is to test and measure. If your mail program continues to be profitable, and you have the marketing dollars available, keep doing it. Have fun with it while you are making a profit. What is better than that?