The thing about tribute bands is they usually have some enthusiasm for the music. When I saw the ghost of Canned Heat it was like watching a group of session players who couldn't wait to get it over and get paid.
There's a lot of these ghost bands touring England and for the most part it's not pretty. Last time I saw The Animals there were several original members, all of whom had been in the band before it was famous. Spencer Davis with Spencer, but no Steve Winwood. The Yardbirds, more or less intact I think, except for those prima donna lead guitarists no one remembers. Herman's Hermits with permanently fixed grins and no Herman. Genesis with only Mike Rutherford, that was a depressing night. There's two versions of Wishbone Ash, but I haven't heard either of them.
For a band to survive the changes I suppose it needs at least one strong driving force - Jagger, Townsend, Anderson and Squire, Ian Anderson in Jethro Tull. John Mayall's still going strong, finding and discarding guitarists.
As well as the Tony Bennett duets album, don't you also have to jam with Joe Bonmassa?