The progress dialog is a requirement, you have to give the user an idea of how long something is going to take and an obvious way to stop it. The status bar is not obvious enough.
As an additional tweak, I am making the "refresh" button on the References tool window force all references to be expanded and the false-positive files to be filtered out. This works no matter what references search strategy mode you are in.
When the user hits cancel, the unvetted files will still be there. There is really no point in throwing away that information. You may think of it as clutter, but heh, you did terminate the search early, and the references you are looking for might be in one of those files. This give you the opportunity to go hunting that you wouldn't have if I removed the unvetted files.