at first I disliked the edit filter, but I've come to use it quite a bit now. I don't always actually click on it, but I shift-click automation envelopes and clips to bring them to the front all the time. I use the edit filter drop-down to make clip automation (I still think doing it this way is a mixing-up of the clip/track hierarchy, but at least it works), and to switch between notes/clips on midi tracks.
Using it to show layers would make sense, as the layers can be thought of as simply another way of looking at the audio on the track. One problem would actually be with clip automation, which couldn't be shown on layered clips. Ideally, the layers filter would be a check-box in the Edit Filter drop down list, so that it could be turned on and off independently from the other parameters.