Were you (or for multi-stayers are you generally) happy with the hotel/stay?
Yes - very much so

Which room did you book and which upgrade did you receive?
Booked King Bed, Main building on breakfast rate. ($179)
Upgrade to Junior Suite in Historic Tower (3804)

How are the rooms?
This the highest (location) suite that doesn't require the secondary elevator. Compared to other junior suites in the Historic Tower, this was fairly small (only one bathroom, one king bed + sofabed, one minibar). Very nicely decorated, two flat screen TVs, very large bathroom with separate shower and soaking tub. Room has views to the east and the south. Firm but comfortable bed and a couple of chairs in the bedroom, desk (including multifunctional printer) and sofa in the parlor. Minibar beverages only were free (1/2 bottle of red, several beers, 14 mini liquor bottles [including Maker's Mark, Bacardi, Belvedere, and Chivas].

Welcome gift: 3 pieces of fruit, 1 L Evian, 6 truffles

How is the exec. lounge?
N/A - there is none.

What was good and what was bad?

Good:
Excellent upgrade, view to south of Wrigley Building, Tribune Tower, Chase Tower, Trump Tower, and Sears Tower (in one shot).
Room was very spacious and pretty well-appointed (one of the best I've stayed in)
Breakfast included (according to Front Desk Manager) on both days.
Great location for finishing up Christmas shopping.
American breakfast (including bread pudding and omelets) quite good.

Bad:
Floris toiletries (I was hoping for at least the Crabtree and Evelyn)
Fog obscured view during the weekend (obviously not the hotel's fault)
Continental breakfast components weren't great, which I'd expect at a $20 price point for a continental breakfast.

Value for $ or Priority Club Points? Would you return?
At the prevailing rate, even without a BOGO, it's excellent. You can imagine how it would be with a BOGO and 3/4 of the cost defrayed on the AMEX card. I'm looking forward to going back there, too, as I'm a big fan of Chicago.

Other notes:

Pictures can be found here. I'm still working on the quality of shots here, but at least you can see that it's a pretty nice spot.