Had this exact same problem wih a 94 GL wagon. A wierd, strong vibration appears between 65-70 mph, and has since the get-go. Despite many visits to the dealer, it was never fixed. The head gasket went out 1 month Before they issued the recall/repair notice. Other than that, it's been ok, though it's been driven lightly. It barely has 100,000 miles.
We gave it to our teenage daughter,and it is the perfect teenage car; being too embarrassing to cruise in, and the vibration keeps her from going very fast, or far.
Have two teenagers. Neither will drive my Taurus which is fine with me. My husband fussed at me this summer for spilling something in the back seat. I looked at him and asked "Do you really think it's going to hurt the trade in value?"! The trunk is full of wheat straw and fertilizer and assorted junk. Absolutely love the radio controls on the dash! The memory button sticks and has to pulled back out, but it did the same on the other one I owned. Shrug.
You're going to wish you hadn't done that when the time comes for her to select your nursing home. ;)