This movie is based on the television series that aired 1965-1966. The movie in and of itself is, well ... just okay, but compared to the other 3 Tammy movies, "Tammy & the Millionaire" is pretty bad. The original storyline is only loosely used. Except for the change from Debbie to Sandra, the first 3 movies followed continuity & storyline very strictly. This film, as well as the TV series, has very little to do with the original. The charm & warmth of the first 3 films is lost on this one. It is very much like 60's campy television, which is great for "I dream of Jeannie" or "The Brady Bunch", but doesn't fair well for Tammy. Debbie Watson who played Tammy in both the TV series, and this movie, just doesn't do the character justice.
I highly recommend "Tammy & the Bachelor" with Debbie Reynolds (the original) or "Tammy Tell me True" with Sandra Dee. Also note; in the first 3 movies the character is named Tammy Tyre. In "Tammy & the Millioniare" she is Tammy Tarleton. I imagine this allowed them to completely abandon the original storyline, as well as the original talent & charm of the other films.