I've seen a Morgan trike "raced" at Lime Rock. The driver was having a good time but stayed in the very center of the track. They certainly look like fun in much the way an old style Se7en is fun - that is not that fast but totally involving to drive.
My wife & I sometimes hang out with the Moto Guzzi owners. They are very appealing bikes. Very Lotus like in some of their philosophies (parts availability, dealer service...)