Seatttle has a great thing going on! I can vouch for that as well.
I spin at the Ann Arbor Soul Club in Michigan. We get around 400 people through the door every month as well: typically, it's folks of all ages at our party, looking to come out, have a good time, and dance to soul 45s. We're coming up on our 3-year anniversary in December, wsg Mr. Fine Wine. As in Seattle, there's no real concern for whether or not we're playing "oldies" or certain 45s championed by certain UK/European DJs. I would say that a decent amount of the folks in our crowd do collect records, and that our night has definitely turned some people on to collecting soul 45s as well. In this last respect, I think it helps our cause that we're in Michigan, where there still are records to be had.
In the "midwest" here in the USA we have the following nights run by "serious" American collectors, plus many more that I'm sure I'm leaving out:
Ann Arbor Soul Club - Ann Arbor, MI
Magic City Soul Club - Detroit, MI
Windy City Soul Club - Chicago, IL
Title Town - Pittsburgh, PA
Gold Label Soul - Lawrence, KS
Hipshaker - Minneapolis, MN
Hotpants - Minneapolis, MN
The Get On Up Soul Club - Milwaukee, WI
North By Midwest - Milwaukee, WI
The Soul Hole - Milwaukee
More funk-inspired nights where you would still here some soul sounds mixed in would include:
Funk Night - Detroit
The Get Down - Milwaukee
Sheer Magic - Chicago