The biggest problem is that people usually try to equate wealth with happiness. I haven't achieved my idea of wealth yet, but many others who have don't seem very happy.
So, to get back to the original question, I define wealth as the ability to live life without financial constraints. Imagine waking up one day and being able to do whatever you wanted and not even think about how much it will cost. This is the type of money that would allow you to pursue your true passions instead of simply the pursuit of more money.
You really can't put a monetary figure on wealth since it's all relative. There are people out there that would consider my E90 an extravagance, but other's who wouldn't be caught dead in such a "lowly" car.
I consider myself fortunate because I was happy even when I was broke. Having a few nice things just makes it that much better.
2008 BMW 535i Space Gray, Black Leather, Dark Bamboo Trim| Sport Automatic with Paddles | Sport Package
2008 BMW M5 (gone, but not forgotten) Space Gray, Silverstone Merino Leather, Madeira Walnut Wood Trim | 7speed SMG | All options
Mods: Corsa Exhaust | RPI Ram Air Intake | H&R Sport Springs | Rogue Engineering 12mm spacers