I live in Anaheim, CA so I'm considering Phoenix and Las Vegas since they are nearby and not crazy expensive.

Welcome to Biggerpockets @Dario Furman You can find local REI groups by attending nearby events here https://www.biggerpockets.com/forums/521-events-and-happenings

I am wondering how Holyoke’s housing market could react to this huge casino right nearby.

I'm seeing that nearby 3 bedrooms like this one have sold on average around $35k within just a few blocks. 

We initially were looking at the Killeen, TX area because running quick numbers showed good cash flow potential on rentals with the nearby army base. 

I %150 feel that the house is worth $155k if its in the market in the summer, plus the near by school is expanding and the neighbors that they often get cash offers (from developers mostly) to buy up the houses for at least 20% more than what its worth.

Plus the house is very old and will definitely need some work when they move out but it has great potential (a nearby house after renovation sold for double the listing price of this one) One strategy is to make the offer based on the monthly income accounting for the maintenance and capital expense (probably no need to consider vacancy, otherwise I can renovate and raise the rent) . 

Certainly, if you get in on the bottom of an upswing in Springfield, you could enjoy some nice appreciation on top of good cashflow, but the area seems much riskier than some nearby alternatives.

I think there a few up and coming areas considering the major development of a solar city/Tesla factory nearby and a massive medical campus that is opening up soon. 

The building is gorgeous with floor to ceiling windows and a large development of houses going up nearby.