You're even on the hotel front (or close to it). You paid for a night in Vegas and DL
substituted a night in Atlanta. On a mechanical delay, you should have received meal vouchers, too. Getting an airline to compensate for "a night of your vacation" is less fruitful than getting blood out of a turnip. It would be reasonable to request to change your return flights at no charge, however. Did you ask to be put on another airline CHI-LAS
? Traveling on low-fare advance purchase tickets? You can always read their CoC (at Delta.com or any airport location) and hold them to every condition therein.