You're absolutely right to see what Delta does over the next few days, and what their competitors do in response. Many travel editors are saying that what is coming could be the most significant restructuring of airline fares--and the arcane regulations that now surround them--since airline deregulation back in the "dark ages."
But be aware that most of the fare cuts will be centered around the now comparitively high "walk up" fares which are purchased at the last minute mostly for business travel. That's because the lowest leisure fares are already so low that there's not much more that can be cut.
What we are likely to see is a simpler structure overall, which, if it does what they intend it to do, will take away a lot of the "should I buy or should I wait" crapshoots you're now facing. We can hope so anyway.
Whatever happens, the old rules are changing, which means that our approach to buying tickets will have to change as well. This is one of those times when anecdotal stories about "what I did last year" and "what I always do" are simply irrelevant.