This depends on what I'm trying to buy; if I'm having to spend a lot of money on buying positional goods, I'm not wealthier.

Before anyone assumes that 'positional goods' means "biggest house on the block" or "huge speedboat", I might point out that "a house to rent/buy in a high school district that doesn't completely suck" and "time with a competent doctor" are a couple examples of de facto positional goods.

I'm aware that we could see a big increase in the supply of that latter in theory, of course... but I'd be willing to bet that it'll be quite likely to see big-screen TV halve in price in the next 5 years, or a mid-market car add most of the features of a 2011 luxury car by 2016, etc. I'd also bet that the relative pricing of good educating, lawyering or doctoring goes up in the same time frame, even taking into account innovations in these spaces (Khan academy, do-it-yourself legal stuff, ...)

For positional goods, it doesn't matter much what happens to the share of the wealth held by the bottom 10%.

Distribution of positional goods is determined primarily by position - the bottom 10% are always stuck in last place for positional goods. There is nothing you can do about that short of making everyone's wealth identically equal.