I see some of the suburbs are very nice there I wonder if it is hard to keep renters since the only business there is tourism or if you get your expenses covered and then some from the busy months?... 

If you take the Riviera Maya for example, which is in huge demand (because you have all the pure investors in tourism on top of the expats), it is very cheap compared to the equivalents in either Costa Rica and North America.Finally, I totally understand your reluctance to invest in pre-construction.

Plus, the Coravirus has had a huge impact on air travel / tourism, which then impacts airlines, which then don't need new airplanes.

No one has a crystal ball, but the climate, tech, and tourism industry boom would lead to continued price growth over long period is what I suspect.  

Besides tourism, there are nearby hospitals and universities to (possibly) drive some demand for this type of housing...Has anyone had success (or failure) with a listing that only allowed guests to book for periods of 30 days or more?

Right now I live in the Yukon territory and usually work here full time during my summers at a tourism company in town.

While I am not sure what Whitestown's stance is, but I bet the smaller towns that are a little further from Indy will be very open to AirBNB and other such services as it creates more traffic and tourism in their areas.

Despite increasing tourism for several years running, income was stagnant or dropping.

Talk to the Better Business Bureau for the area to determine what level of tourism is for the City.

I have no idea what tourism is like in your market, but you should be worried about how many tourists you get at all times of year, and use that to calculate vacancy factor.