I saw them in 1975 (November I think, maybe October), what I consider the classic lineup (Jeffrey, John, Barriemore, Martin, Ian); I saw them, hmm, in the 1990s I guess, and only Ian and Martin remained. The drummer was a very goofy blonde hippie young guy; Dave Pegg was on bass. The audience was a bunch of aging fans, plus their adult or teen children.
Ian Anderson's glory days are far behind him. But I'd still rather see Tull than about 99.5% of other Rock & Rollers. I can count on my fingers how many bands I'd walk across the street to see for free, much less pay $50 for the deal.
But yes, from their inception until the end of the 1970s, the band was excellent.