I feel that looking up the dates for one of your previous contests is a bit laborious.
Let's say you're looking at one of your old contests data in your user profile and you suddenly feel like knowing exactly when (the date) it happened.
You can't immediately get the contest date from the rating graph or the contests tab.
You have to go to the contest link. But it's not over yet. You now need to click on the Announcement link. After which you have to scour the announcement post to find it. I hope I haven't missed anything.
So, I think it'd be better it if the contest date were a column in the Contests tab (in the user profile).