I recommend these places of attraction:
Millennium Park
A view of Navy Pier's Festival Hall looking west
Navy Pier
Skydeck Chicago's The Ledge
The newly restored Tiffany Dome at the Chicago Cultural Center
Chicago Cultural Center

The Art Institute is excellent.

Instead of the bus tour, how about the Architecture Foundation River Cruise?

With 2.5 days, you should be able to see a couple of museums. The top ones for me, in order of preference, were: 1) Museum of Science and Industry, 2) Art Institute and 3) Field Museum or Shedd Aquarium (toss-up). Since you've visited Chicago previously, you probably already know to get to the museums when they open as they get crowded fast!

I also think the Architecture Foundation River Cruise would be better than the double decker bus tour.

We had a fun evening at Second City. If you are there on a Monday night, the Improv All-Stars show is real improv and tickets are less than $20 each.

If you take the bus tour, be prepared to spend a lot of time sitting in traffic. The AF river cruise is excellent.
Restaurants? What type of food do you enjoy? Chicago has it all.

It's impossible to recommend a restaurant without knowing your budget or food likes/dislikes. You can check www.chicagoreader.com or www.chicagomag.com and search listings by neighborhood, cuisine or price.

As for museums, what are your interests? In addition to those already mentioned, there's the Oriental Institute on the campus of University of Chicago, the Chicago History Museum in Lincoln Park and the Frank Lloyd Wright District in nearby Oak Park.

If you're trying to have an adult weekend without kids, do not go to Navy Pier. I'd also avoid the Skydeck at Willis Tower. Instead, you can head to the lounge on the 96th floor of the Hancock Building for a cocktail, watch the sunset over the city, then go someplace for dinner. The restaurant in the Hancock is just so-so for the price and there are better places a short walk away.