Similar story, here. My first bass was a Lotus, and to be honest, it served me pretty well. However, my second year in college, my band won a battle of the bands with some decent prize money (store credit at Coyle Music, in Columbus), and my initial plan was to get a better bass with my share of the funds. Nothing really spoke to me, though, so I think I ended up getting some PA speakers. But, this kind of got me in the hunt for a new/better bass, so I tried out every bass in every store I could find. Some basses had me interested, but nothing really spoke to me until I picked up a Thunderbird. I recognized the shape and knew the name, but didn't really have any preconceptions about Thunderbirds, in general. But it spoke to me immediately. From the first few notes, it just really felt "right," and thus began my quest to own a T-bird. I had very little funds at this point in time, but after setting aside gig money and borrowing from one of my roommates, I finally bought a new Thunderbird in 2001. Man, I gigged the heck out of that bass for about 12 years or so. It still remains one of my prized basses, and it has far more gigs on it than any other bass I own.
FWIW, I will note that I have since played a bunch of other T-birds, both older and newer, and for whatever reason (probably my familiarity with this particular bass), my own '91 Bird remains my favorite. It has a super thin neck, ebony board, and I believe these may be the single-coil pickups.