Nightbird was a little blunt, but fairly accurate. Look back in this forum and you will see this same type of question twice a week.
People get sucked in by the whole "make real cash playing a video game" hype and then get frustrated and quit.
A more complete response is that almost everything contributes to health gains. I have just over 120 and I am at 3.9k in handgun with the associated evade, agility, etc. that come from playing to that level. It would cost a bit just to chip up to my level these days.
There are not that many players in the 200+ range, and to chip up to that level would be insanely expensive under the current system.
Even if you do chip up, you still can't chip in attributes. They also play a roll in things. After all of that, it isn't like the money just roles in.
The higher the level you are, the better you're chances are of looting more valuable items, but you also end up spending huge money on equipment and supplies.
If you want to profit, buy a Land Area. Otherwise, it's a game. Play it and have fun.