Without a doubt the closest exoplanet to our solar system that could be habitable is Proxima Centauri b. Only a little over 4 light years away, the star system will be the first to see mankind. There is no doubt that extensive mining and possible colonization of this first way point to the stars will make even a hostile planet surface valuable.
An entire planet has a lot of real estate, so exoplanet claim deeds cover a wide range of tastes. Everything from nation building to just having your own private exo-ranch!
Since we know so little about the surface of exoplanets, it is impossible to estimate their wealth potential. All the riches and wealth ever found on earth no doubt can be found on any exoplanet, except these riches have never been touched by sentient hands. (Probably.)
Image Credit: NASA / JPL / Caltech / IPAC / IRSA