Reminds me of the most recent conclusion I had come to regarding Groupon: it appeals to broken businesses. If you can't get new customers by simply lowering prices (instead of offering a Groupon), then your business is on very weak ground. Leveraging Groupon's email marketing distribution for a one time boost is not going to fix this fundamental problem.
Forget lowering prices, if you cannot get customers into your business than you really need to take a step back and review your current marketing efforts.
What can be done to get more of your target customers in the door - and to keep that up on an ongoing basis?