Way too expensive
Not to waive my e-9enis or anything, I just want people to know where my opinion is coming from and how much experience is backing it up. Computers are literally my entire life. I've professionally worked in the general "personal computer" field since I was 14 (I'm 23 now) and in middle school. I broke away from the shop I worked for throughout high school when I was 18 (the owner was a complete idiot) and started my own on site computer repair and consulting business. I now have a successful business with a few guys working for me. My personal expertise/passion/love is in home computers, more specifically, computer hardware.
To the seller: No one feels your pain like me my friend, I've been in the EXACT same position. When the business took off and I finally had the disposable income to build my dream computer, I went ahead and pulled the trigger on all the parts (from newegg.com if anyone wants to know a good place for parts). All in all it cost me about 4 grand. 2 RAID (stripe) 10,000 RPM raptor hard drives (solid state weren't really available at the time), ridiculous processor at the time, fancy memory with digital readouts and beautiful heat syncs, a video card so huge I had to choose the case around it, speaking of case I even went for a top of the line Lion-Li (the Ferrari of cases), yada yada yada... I even bought a legit license for Vista Ultimate instead of downloading it. Well long story short, I guess I had it built up in my head so high that it never really could have met my expectations and after a month or so I was really unhappy with it. I wasn't into gaming and was starting to travel a lot so I decided a MacBook Pro would be a much better machine (and it ended up being just that). The computer was so new I figured I could get at LEAST 2/3's what I paid, and at the very least, I could get 1/2. I was in the best possible position to sell it because I had plenty of connections to existing customers that needed computers so I figured it would be pretty easy. Long story short I ended up having to sell it for FIVE HUNDRED DOLLARS! I was SHOCKED. Since then I started paying much closer attention to the resale value (or lack thereof) of computer equipment and I've learned that it even puts cars to shame. I dare say that NOTHING (besides food) loses value faster then (most) consumer electronics. When people come to me now with laptops (PC not Apple, Apple's do much better) they want to sell, and it's been around 6 months since they bought it, I have to tell them all they can reasonably expect is about 1/4 to 1/5, if not much lower, then what they paid. At first it may seem to go against your intuition, as I read above you stated the same thing I used to think. It's not like the parts don't work as well now, it's not like you have to worry about "wear and tear", they're virtually identical to new no matter how much they've been used. Hell, the only moving parts are the hard drive and fans. It's got more to do with the fact that technology is moving faster and faster and parts are being outdated in 2-3 months. Stuff that costs $1,000 now will get handily beat by stuff that costs half that in less then a year. So basically it comes down to why buy used when you can buy new?
Onto the computer in question... Between Macs and PC's, PC's have a far worse resale value, and among PC's, Alienware's are among the bottom of the pile. You paid a few hundred for a name that gets you absolutely nothing now. Potential customers interested in a computer for gaming will typically build their own because they need absolute maximum bang for their buck. The kind of customer that's interested in high performance and is willing to pay extra for a name brand isn't interested in a used computer, they'll just as soon spring for a brand new one. If they're in the $1200 range then they can get a brand spanking new Alienware Aurora with a Core i7 (a FAR better processor then the Quad Core), 3 gigs of DDR3 memory at 1333Mhz, even better liquid cooling, Windows 7 Premium, and dual ATi Radeon 5670 video cards with 1GB of GDDR5 memory each for $1299 right now. That's the full retail price too, meaning with a little hunting around it can be found for even less. And don't forget the new machine will have a full warranty to cover any bad parts while the guy buying yours has to take a huge gamble that nothing goes wrong. You can find this deal right on Alienwares site btw.
Bottom line? Consider yourself lucky if someone will pay $500 for it. Period.