Thanks guys!
Cory: Definitely go for it! We were thinking about you guys during the trip. This was an amazing trip for our whole family, and the kids are still talking about it every day. There's no doubt that this will be a trip I'll remember for the rest of my life. As they say in the Mastercard ad: Priceless.
Our kids are 13 and 6 years old. For us, this year seemed like the perfect time since our son is old enough to really get a lot out of it, yet our daughter is still young enough to be excited to spend 3 weeks in a tent with mom and dad!

We also planned this trip about two years in advance to get the time off.
I'd say go whenever you can get a long enough stretch off from work. It was definitely nice having three weeks, and we used every second of it.
We had several days right at the start of our trip that were WX no-goes, and later there was some really bad weather through the Yukon that kept us in interior BC for several days. Having as much time as we had, we could make lemonade out of those weather lemons and got to explore some places we probably wouldn't have seen otherwise. Monkman Provincial Park, etc. Hanging out at the airport staring at weather on the iPad is no fun for the kids. Having enough of a time buffer allowed me to just relax and enjoy the place we were at instead of stressing about making headway.
The trip can seem a little daunting at times. The biggest factors for me were weather (obviously), not being familiar with the terrain, and the distance between fuel options. I'm a planner/preparer, so I like to know what's ahead. The way up was a lot more challenging for me, partly because the weather was iffy, but also due to the fact that it was my first time through. On the way back, I knew the terrain and had a better handle on how the local weather behaved, so even if we had some weather I felt a lot more confident. The kids and I actually made it back from McCarthy to southern Oregon in 4 days without any drama.
Alaskan Flight Service is totally awesome! Being able to walk into an actual FSS and talk to a real human being who actually knows the local area makes you realize how much we've lost here in the lower 48.
Cost-wise -- I'll have to get back to you once I do the final accounting.

Most of the cost was fuel, of course. Not much you can do about that. We camped more than half of the time (13 nights) which saved a lot of money. Hotels are expensive up north! We also made our own food as much as possible, which saved a lot. We tried to be scrappy: borrowing a bicycle to get to a (much) cheaper rental car place in Fairbanks, for instance.
We didn't have a single mechanical issue on the entire trip! Pretty amazing. I carried a bunch of spare parts, tools, pump, tubes, etc. but didn't need to use any of it. Not bad for a 55 year-old airplane!
Everyone had their own backpack with their clothes, gear, sleeping bag and pad, etc. This way we could fairly easily get from the airplane to a camp site without having to make lots of trips. The only downside to this arrangement was that backpacks don't pack very well in a plane. All those straps get caught on things, etc. A better arrangement might be some sort of light duffel bags with carrying straps, but the basic idea was good.
For cooking, we used a Firebox wood burning camp stove. This way we had an endless supply of fuel and didn't have to bring a bunch of stove fuel, worry about it running out, etc. (We did carry a backup MSR micro rocket.) I've converted to using the Firebox for backpacking as well if I'm out for more than one night. It's heavier than my MSR stove, but you don't carry any fuel.
Finally, I have to say again that the BCP community was incredible on this trip! Having the Delorme along with this thread helped us meet so many people we probably wouldn't otherwise have met: "Lurker" Larry in Fairbanks, Dieter and Karen in Fort St. John, Gordon and Vicky in Quesnel, TyredWagon who called us up on the radio as we passed each other between Whitehorse and Watson Lake and many others. Some we sadly just missed: Nizina, A1Skinner. Next time!
Thanks again, everyone!