It is difficult to say exactly what is right for you without a photo. From your description it sounds like you are in very good shape but are starting to notice subtle changes in your face. Thermage can be beneficial for skin tightening, especially in a younger population with firmer, tighter more elastic skin. For these patients, results tend to be better.
Patients, like yourself, who have little to change can only expect a minimal difference after treatment. The other consideration, however, is that I have many patients who love Thermage for what they call maintenance. in other words doing Thermage proactively once a year to maintain their good skin tone and slow down the aging process. In following these patients over several years, they really have exhibited very little aging. So maintaining your skin with non-surgical procedures will provide benefits for the future just like your daily skin care will fight the aging process and help maintain the skin. Consider them both as part of a complete anti-aging package.