Not as much as you might hope. The uniques/day will tail off as time passes and the name gets taken off of toplists and links get taken down and it gets reindexed in search engines with a parked page, etc. I had the same thought when I had to park the last proxy site I bought, and since the first few days it's been a roller coaster between 50 cents and $5-$6, with uniques mostly going down from day to day. I think if you could get like $500+ for the name based on the parking, you'd probably do well. The problem is that most people are going to want a months worth of stats, and they can see the uniques tail off day by day. Also, you realistically can buy a proxy site for that much or less that at will do that kind of revenue parked, so I'm guessing the reverse is true. If you do sell it, let me know as I'm kind of curious about the sale of a name like this.