How much is a 144 worth nowadays, as project cars go?

They aren't really worth anything, especially compared to 120's & P1800's. They lack image, they aren't sporty looking like P1800's or Amazons and they lack the safety image of the 240's. I think they combine the best elements of all three: they handle & weigh similar to 120's & feature the same primary safety elements, but have space & practicality of the early 240's with some of their secondary safety elements. '67-'69 cars are rather special, they have a bit of extra metal in the A & B pillars. '70-'72 had some improvements such as bigger upper ball joints & bigger tie rod ends. '73's got the 240 style dash, tail lights & bars in the doors, the metal used in the doors & panels got thinner as did the glass. '74's got the new safer fuel tank layouts as the 240's.

What else should I be looking for?

Just look out for salt induced rust. The early models rust less than the later ones. Only real problem spot for rust is at the bottom of the windscreen & the rear screen where the drain holes air (like 240's).