Jim I was actually just thinking that last night, space-wise it would be easy to add more shelves but the way the Detolf is designed inside holding the glass shelves is like those welded steel wire clothes airers, painted by Ikea and so you'd either need to strip the paint off, weld in more shelf support wires then repaint or perhaps work out a mechanical bolt-on addition..I've attached a photo and you can see the shelf support 'wire'.
I'm thinking of just buying another one hehehe..