I had no idea that any of that was even possible in the game until you mentioned it.
I was given a couple of gift cards recently to a store that sells games, so I actually just picked up GTA V over the weekend. My draw to GTA has just been the casual open-world/sandbox exploration aspect of it. Never really got into the story, missions, or "beating the game". I love just driving around hijacking cars, evading police pursuit, and flying jets :)
It is interesting to see that there is a whole economy side of the game though. What's the point of investing in it? Is it purely an in-game reward?