I'm wondering if you could have something strange running on your laptop. Or if Xirrus might be giving you bad info. I'd be curious to know if you see those same very strong SSID's if you take your laptop to another location...another neighborhood.
I'm not personally familiar with Xirrus Wi-Fi inspector. I use inSSIDer. You might try it to see if you get the same results.
Good luck, and I'll be interested in any news you provide, and/or if anyone else here on the forum has other ideas.
Edit: It's not uncommon for wifi to be less-than-great when trying to use it through multiple walls or floors. My solution is to use two wireless access points. I use my Actiontec at one end of our house and another WAP in the basement at the other end of the house. That gives us solid coverage throughout.
You might consider solving your problem by setting up a second WAP upstairs.