Duke said it better than I can. FWIW Wilson has shown with Audio Research a good deal in the past and ARC has Wilson speakers in house. So despite the dips in impedance, Wilson's are 'tube friendly'.
The Wilson Watt has long been an example of the phenomena that Duke presented above. The speaker had a reputation some years back for being bright- around 2KHz. There was a tweeter resonance at that frequency, which anyone with a transistor amp would tell you was uncontrolled. The tweeter did in fact have a resonance, but Wilson controlled it with a 'band reject' filter, tuned to 2KHz, which caused the speaker to have a 2 ohm impedance at that frequency. The rest of the speaker was about 8 ohms; transistor amps would dump power into that filter, and tube amps would not make any power due to the filter. As a result the speaker sounded great with good tube amps, bright with transistor amps.