Barnstorming doesn't build a team following though (and they have three teams who did that last year... or maybe two. I can't recall if Cleveland ever played any real "home" games).Maybe the fixed venue and regions are part of the problem. In the early days of baseball and men's fastpitch in the time of Eddie Feigner, barnstorming was the way to go.
Imagine a league where the games are played at existing college facilities. A four-day barnstorming stop for two teams might include a two-day clinic for local players to learn from the pros with game tickets included in the price. Maybe an exhibition game against the host team. Fundraisers for the local rec leagues where they get a cut of ticket sales. These types of things would only work if you could get games into many more places than fixed venues can provide. Not to mention expanding the likelihood that people would come out to see a game if it were in their neighborhood. Not eight times a year, but once or twice. Think the Bandits would draw a few fans who would come out to see Aleshia Ocasio pitch in Gainesville? I think so.
What you mentioned is a fun gimmick to draw a decent crowd once in a while, and stuff like that could help, but that's not how you sustain a league.
They need exposure. They need a twitter account people can find. If you type in "NPF" into the twitter search bar, the #1 result is "National Psoriasis Foundation" and the NPF twitter account doesn't even show up because "NPF" appears nowhere in their name or handle. Because nobody there has the first clue about how to actually run a league.
Imagine if, instead of @MLB, the Major League Baseball account was @probaseball. OK, even that doesn't really demonstrate how stupid the NPF is because at least the word "baseball" exists in my example. They don't use the word "softball," so if you search the most important word you won't see the league's twitter account pop up.
Of course, the account itself is worthless anyway. They didn't even do regular, live updates of their championship series in August.
I can't say for sure if a pro softball league could be viable, but I am certain that there are measures the NPF could take to improve their lot in life if they were at all competent.
EDIT: To be fair and somewhat kind, Bandits games are a fun experience, and that do a lot to make that game day experience a lot of fun. But it's like they're trying to keep this s*** a secret with how bad they are at informing people about the product.