To preface, I'll say that my experience with the wealth system is based more on reading and thinking about it, since I've only played one off or short term games in Modern, with one campaign just starting.
I definetly agree that some sort of abstracted system for wealth is a good thing in a world where most items are bought on credit, but I have some strong misgivings as to the way things are set up. As it stands now, your wealth has very little to do with the actual job that you perform, and is based on your level and making Profession roles as you go up. Which means that the longer you go up in levels, the higher your wealth goes. Add to that that you can buy anything up to your wealth level without affecting it normally (until you hit that DC15 cap for cost), and potentially someone could work at a fast food resturant, go up in levels in their part time job as a shadow chaser and wind up being rich enough to buy out the store.... And that's assuming you didn't pick up any wealth bonuses from beating monsters or windfall feats. This doesn't sound right to me...
On the other hand, as RangerWickett pointed out, people with high wealth bonuses still lose points when they try to buy expensive items, even if they could easily afford it. But you could buy an unlimited amount of items costing DC14 or less. Again, doesn't seem right to me.
A better solution I think would be to have a person's wealth bonus set by their job, plus any Windfalls or 'treasure' bonuses they get. Have any iems purchased up to your wealth level cause a temporary loss to your wealth (Maxing our you credit cards for that new car or such), which would recover at a set number depending on your total wealth bonus, say recovering 10-25% a month maybe. Anything you try to purchase over your wealth limit permanantely reduces your Wealth, as you are stretching your credit/available wealth to it's limit. And as Ranger suggested, dump the DC15 cap. Multi-billionaires can afford to fly to Europe for breakfast on a whim without having to cash in their stock options.
Just my +2 Wealth check
