Linear investments for linear gains, huh? How hard would it be to boost Res and is there a stat cap? If money can buy xp, and xp can be used to boost Res, which develops moar moneys... playing banker would make for a dull LP, though .
Still, having a couple of research-monkeys to instantly develop captured ground without a massive investment of manpower could be nice. People developing land aren't available to defend it, i assume?
The money-thingy actually is rather sensible. Currency is a rather flexible concept, afterall. Ouki is produced by ley-lines, so it's assumably some kind of distilled magic. If it's portable enough, it's just as good as currency as precious metals/squirrel skins were historically. Might not even be a case of buing stuff as much as making it from distilled magic.