Good thing that I'm not using the Dark Sun rules in my new FR campaign.
I want the players to have to decide "do I keep my +2 flaming longsword, or do I upgrade it to a +4 keen longsword?" with the inherent bonus rules.
Having the crit bonus still be attached to the original bonus of the weapon gives the player some small incentive to trade up. Otherwise, it becomes a game of "I got my +1 weapon of xxx that synergizes well with my PC, there's never a reason to acquire a different +5 weapon".
