I've found that Glad I Did/Wish I did posts are a great way to quickly share with others what worked and what didn't on our cruise. They're also really helpful to refer back to over the years when preparing for our next cruise.

Glad I did NOT bid on a Stateroom Upgrade
I was very tempted to bid on a stateroom upgrade. There were Concierge Class upgrade bids starting at $100 per person. However, after some research on the Concierge Class, I learned that there wasn't a big incentive to upgrade to Concierge Class on the Celebrity Millennium Series ships. The stateroom is no larger than a standard stateroom. The only extra features are a Celebrity embossed key holder and an "Exclusive Welcome Aboard Concierge Class Lunch" (we actually would have enjoyed that lunch). Also, I had selected a neighboring stateroom with Aaron's parents. I would have bid to upgrade Aaron's parents as well, but there was no guarantee that our rooms would still be next to one another, and there was also a risk that one stateroom would get upgraded while the other would not. It's a risk that I've taken with my family in the past, but give that it was Aaron's parents first cruise, I didn't want to accidentally get our staterooms moved to opposite ends of the ship.