Minor league or not doesn't seem to affect prices. The Saint Paul Saints charge just about the same for beer and food as a minor league team as the Major League team does in the Minnesota Twins. When the Loons were still USL and they played in the suburbs very few people went to see them, but they had their devoted fans that filled it up. They've kept their prices fairly low with the new stadium in Saint Paul. The Minneapolis area is much more soccer mad than Milwaukee, I don't think there are enough die hards to keep them afloat without reasonable prices, especially on beer because it is Wisconsin.
If the prices were reasonable and I had something else I was doing in Milwaukee maybe. I highly doubt I'm going to drive the 80 miles just to watch a soccer match. If my kids were into it I would go, but they don't care about sports at all.