It would be awesome to consolidate the trim tool to just a simple "one does all" trimming tool.
*If you want to drag and trim an event over the next one, simply put the cursor to the left edge, and pull to the right.
*If you want to trim an event back over the previous one, simply put the cursor to the right, and pull back to the left.
*If you want to trim an event back or forward to create an empty space or gap in the audio, just put the cursor at the edge and trim it back.
This could be implemented with say an on/off for underlying audio (I have another request for this). When toggled on, you have the other tool options to trim all audio; top and underlying. When off, it just becomes a simple trim tool.
This would take the guess work out of moving the cursor up or down on an event to choose the right trim tool. It's essentially making you use 3 different tools to do one job. It seems to make more sense to just have one tool do all of those tasks regardless of where the cursor is on the event.
(On a personal opinion, underlying events is over complicating things... That's what crossfades and the envelopes of those crossfades are for. Or, just put the two events on separate tracks if they are different events. It will give you better control.)