Even though they were very different characters, I think Barnabas and Mr. Spock had some things in common in terms of the way fans reacted to them back in the Sixties. Spock was so cool, intellectual, and controlled, it really seemed to fan the flames for a lot of viewers, and the writers were wise to include a couple of characters onscreen who could act out that passionate response--notably Christine Chapel, incarnated by the fabulous Majel.
With Barnabas, I think the way Frid played him with those silent, big brown eyes staring in anguish up at the sky, brought a quality of what back then we called "soul" to the character. And, in the Sixties, Soul was very, very sexy! I think how fans reacted to Barnabas was due entirely to Frid's performance, particularly the non-verbal parts (though his voice was very alluring, especially at moments when he was more confident and in control of the material). On paper, Barnbas was a regular cad in the beginning, and even in his most altruistic moments could always drop everything if he got some Sweet Young Thing in his sights. On screen, with Frid's performance, the character was transformed, and fans voted across the nation by keeping glued to their TV sets at 4 p.m. every afternoon.
Thinking about what a huge impression Spock and Barnabas made back in the Sixties and looking at today's teen crushes--Justin Timberlake, Tom Welling, a bunch of other guys whose names escape me--really slaps me in the face with how much times have changed since then.
G.