I dunno about getting them to upgrade you even if you pay the difference. Never hurts to ask, though! (Of course, the amount I paid for my original MBA is now the price of the top-of-the-line, but I still got the base model )
I'd agree with others in the thread about playing relatively dumb and being a little coy about what you want. If you go in saying "This computer doesn't work, I want a better one," they're less likely to help. I went in, explained every issue I've had with my computer in the 18 months I've owned it, showed them my screenshots and videos, and then gave a rundown of the replacement and repair history, with them verifying my statements in the case history of my machine. The genius went in the back, talked to a manager, came out and announced they would replace it with an "equivalent model." I sort of tipped my hand when I asked to verify that equivalent meant the current base model, not another Rev A, but that's the closest I came to asking outright for a new computer. If you go the subtle route and it doesn't get you anywhere, no harm in asking for a new one, I suppose, but I'd do my best to lead them gently to that conclusion than making demands.
I'd agree with others in the thread about playing relatively dumb and being a little coy about what you want. If you go in saying "This computer doesn't work, I want a better one," they're less likely to help. I went in, explained every issue I've had with my computer in the 18 months I've owned it, showed them my screenshots and videos, and then gave a rundown of the replacement and repair history, with them verifying my statements in the case history of my machine. The genius went in the back, talked to a manager, came out and announced they would replace it with an "equivalent model." I sort of tipped my hand when I asked to verify that equivalent meant the current base model, not another Rev A, but that's the closest I came to asking outright for a new computer. If you go the subtle route and it doesn't get you anywhere, no harm in asking for a new one, I suppose, but I'd do my best to lead them gently to that conclusion than making demands.