Here is some things I have thought of, being born and raised in Denver.
September 21st, the weather will be spectacular. Mid 70's and sunny (typically) we have 300 days of sunshine and that is our dryest season. Plenty to do with the family if you are making it a family vacation- the aspens will be turning so the mountains will be beautiful.
I have tickets for the game (no extras sorry), if you need them Craigslist or stubhub are great online place to find bronco tickets- also scalping is not illegal in Denver so people stand outside and sell tickets. I also work with a bunch of Broncos season ticket holders, and I will see if I can grab a couple sets- if I do I will post them....
Stay out of the South End Zone, if possible. This is where the crazies are and they will make your life hell- and not in a fun and games kind of way.
The best thing to do for games- especially if you are planning on staying in a hotel, is stay a bit away and ride the Light Rail, hotel will be much cheaper. It is only $3.50 and will take you to LoDo ( the main bar and restaurant district) and also has a stop right in front of Mile High.
A great site for Denver- stuff to do, places to go- is 5280.com. this is the city's magazine, which has the best restaurants and such. A good place for nightlife is westword.com it shows all the local happenings. I will list more as I remember them.
I am willing to help get a SR tailgate going at either the stadium or my house which ever would be better. I have enough grill equipment for a big event and I would love meeting and hanging out with you guys. This is only going to be the second time I have ever seen the Saints and I cant wait!!!
Geaux Saints!