No, it isn't valid. The legal case is debatable, borrowing agaisnt future and probable income streams is not. Municipalities borrow against future income streams all the time as does pretty much any other business. This is commonplace, they are called municipal bonds. Say for instance the City of Des Moines borrowed money to build a Monorail. Those bonds would be guaranteed by the income stream and the monorail assets. Being a risky project investors would require a higher yield and the bond would be appropriately priced. Let's then assume, no one used the monorail and there was no income stream. Those bonds would be worthless and the investors would lose their money. In that case there is no one to cause damage, the public chose not to ride the monorail, it is the investors own fault for investing in a stupid project. In Iowa State's case, there is someone at fault if that contract is not delivered upon, and it is the other universities.
Now you can argue all you want about the legalites of if ISU could win that arguement. What cannot be argued rationally is that Iowa State is in the wrong by borrowing against future income streams that at the time were highly probable. It is done everyday, thousands of times by businesses and organizations everywhere in the world. Nothing would ever be constructed or financed otherwise.