It's not really buying the ship that's the issue.
It's the incentive for FD to nerf the entire economy to make buying ships with real money for attractive.
Not really true.. Let's look at what you get in game, and at the store..
In game; A flight model, a module definition and shape
In store; a graphical scheme and if available, shape additions
There is no reason to say that expanding the shape model and selling it in any way effects the E.D. experience or game play. Once the module allotment and flight characteristics do not change.
Let's look at an example.
I own a Corvette. I buy a scheme and shape model for it. It no longer looks like 'your' corvette, but flies the same and has the same gun placements and same modules.
How would it effect you or your gameplay?