The first attempt to bring down the WTC was in 1993, before the US intervention in Kosovo. It stands to reason that other "grievances" were more important--US support for Israel, US support for conservative Arab monarchies, the US interventions in Lebanon, the fiasco in Somalia, etc., along with their general hatred of "infidels" and "Crusaders."
The "Martydom Videos" recently released by Al Qaeda have at least two of the 9/11 hijackers saying that the US intervention in Kosovo was on their list of grievances that caused them to participate in the destruction of the World Trade Center. These videos were made about a year before the attacks, while these hijackers were still in training.
The fact that we intervened in Kosovo in their favor completely escapes them. I have to conclude that they don't really care. They are going to attack us, no matter what we do.
Appeasment never works. But it extra-especially-doubleplus doesn't work when your enemy is crazy. The only acceptable end point for them is for us to be converted, enslaved or dead. If we're not willing to come across with one of those three conditions, they aren't interested in our efforts to appease.