Lots of great points made already, but the one thing that is the deal breaker for me hasn't been mentioned. When I stay at Universal, I love that you can walk. I love staying on property with everything all right together. That and EP are the two reasons for me to bother with a hotel at all and not simply rent a condo or house.
We don't always walk, and I've taken buses from CB before without any issues, but I love having the option to walk. We find the walking path relaxing and enjoy strolling along it in early morning, and it's so nice to be able to just walk out your door and go. The boat ride is also nice, but we love that if there isn't a boat / bus ready when we are, we can just go. Enjoy taking the bicycle gondola carts as well. Although, you have to pay for those.
With kids, depending on ages, walking may not matter to you at all, but December will be great weather for walking.
I will also second all the people saying book at least one night at one of the Premier hotels for EP. We did that our first trip, booked a throw-away-room, as we actually had a condo off-site, and it worked out perfectly. One night gives you two days of EP, the day you check in and the day you check out.
Also, second getting one AP for the discounted rates if any are available. That could save you more than switching to Dockside would. You can check the rates from the link found in the AP Resort Rate thread here and can book the AP rate room without having your AP yet. You just need to have the AP by your stay. Only 1 person in the room needs an AP to get the rate. If you guys decide you like Universal and might want to come back, you can upgrade your regular tickets to AP tickets at any time as long as they are still good. It's a huge savings over paying for two sets of regular tickets each year, but for the room rates, you only need one AP ticket.
I've not stayed at Dockside as I have no desire to stay "off" property, but CB I've stayed at a few times and always enjoyed. It's really nice, especially for a value. It's more on the Disney Moderate level than a value, and I guess now that they have added Dockside and Endless Summer as the new value hotels, it being a moderate is more accurate. I would checkout the AP rates for it. Not sure availability or price difference for your dates, but I'd do it over Dockside. The theming is amazing. The views of Volcano Bay are great. The pool has a lazy river, and although it is a long walk, you can still walk or you can take the boat to Sapphire and then walk the last bit, so there are options besides the bus if needed.