When I came across the game again the other day I was curious to see if his statement that no engine would find 24.Bg5 is still true, so checked it out with Komodo 8 and Stockfish 6. Neither engine found it! ...at least not after 15-20 minutes or so. In fact, Komodo 8 dropped its evaluation from slightly over a Pawn to a little more than half a Pawn when I actually played the move.
After spending a couple of hours looking at this position with Stockfish and Komodo I was unable to come to a clear conclusion about Shirov's 24.Bg5 even using engines that are much strong than whatever version of Fritz he was using back in 1997.