I agree I-69 is the top priority in the state. One interesting thing in the I-69 plans being discussed is whether to rebuild or keep some of the existing SR 37 interchanges in Bloomington. Personally, I would favor keeping them as they are for now and upgrade the road going north.
Originally, the I-69/I-465 south interchange and a couple of miles of I-69 were planned as a Major Moves project (i.e.the 2012-205 timeframe), but that plan seems to have been dropped.
As for the proposed I-67 (or US 31), I hope they incrementally upgrade it by building interchanges at old SR 47 (236th St.), SR 28, SR 18, SR 218, and Peru. If one interchange could be knocked out a year, the road would be much safer. With only 7 traffic lights remaining, I fear more of those high speed tragic rear-end collisions like the road has already seen. A slow, steady upgrade would not break the bank.
As for US 31 itself, north of Peru, the road is modern, and I agree would be relatively cheap to upgrade. Mainly just a few interchanges, bridges, and cul-de-sacs. From Peru south to old SR 47 , there are a lot of driveways and businesses on the road. South of Kokomo, one side of US 31 is the still the old wavy carriageway which would probably need to rebuilt to modern standards.
The other two top priority roads are I-265 and the Illiana Toll Road, of course. Presumably these would be funded thru public-private partnerships.