I, too, was not completely satisfied with the Wealth mechanic as-is, so I created another advantage called "Connections" which only deals with the buying and selling aspects of Wealth. It has 3 levels:
Bourgeousie, which sells at 60%;
Gentry, which sells at 80%; and
Nobility, which sells at full value. The point costs have subtracted the costs for starting money as per
this thread, and Wealth has been modified to state that each level includes the appropriate level of Connections for the advantage levels. The disadvantage levels are not modified.
I did not create a disadvantage for Connections; I figured Social Stigmas would suit for that.
(I do not have my document in front of me, so am going off of my recollections of what I wrote down. I will edit this post if what I wrote is inaccurate.)