<In my opinion, Fischer may have actually been even better suited to 1.d4 than 1.e4.>

Fischer was intellectually wedded to 1 e4 -- not that I am telling you anything you don't know. He was the last of the opening absolutists, the last really strong player to believe there was a "best move" even in the starting position. I think his use of 1 c4 and Alekhine's and Pirc's at the end of his career was purely pragmatic. If he had kept playing he would have had to broaden his repetoire. But I don't think he ever would have played 1 d4 with white or say, the French or Caro-Kann with black. He just didn't believe in them!

I think you have a point re his style. The Ruy was almost perfect for him -- pity we never saw him play it against Karpov! That would have been fascinating. But obviously he loved forcing lines too, and 1 e4 gave him a lot of scope for those.

In general, (and I know you and <danielpi> discussed this in detail) I don't think you can decide that a player should choose 1 e4 or 1 d4 based on whether you characterize his style as positional or tactical. Karpov was a tremendous 1 e4 player, while Kasparov and Shirov made their names as attacking players using 1 d4. Kasparov liked to build up his attacks into great crescendoes, while keeping the position as complex as possible (who would have believed that 4 a3 in the Queen's Indian could be an attacking move?), while Karpov and Fischer tended more towards multiple sharp little struggles with clear resolutions within each game. Maybe that is the difference between 1 d4 and 1 e4 (to the extent there really is a difference) -- 1 d4 tends more towards the former type of game, and 1 e4 the latter.

Looking at Fischer's opening stats, it indeed looks like the <1.e4> is the (second) best opening ... when Fischer is White. When Fischer is Black, <1.e4> turns out to be the (second) worst way to open a game!!! (In both cases, <1.e4> trails <1.f4> for the ultimate best/worst honor.)