My honest opinion?
Go for mining, not resale value. If you sell it in the future, part it out, don't sell it as a whole rig. You'll generally get more for it, especially if you have dual or triple high-end cards in it. Not many people are willing to pay such a premium for cards they'll never make use of.
With that in mind, I would suggest the following changes:
- 1GB of DDR3 ram, the cheapest you can find. Should be about $13 shipped.
- 250GB HDD, $39.
- Cheap generic case - just something that works for mounting a motherboard and PSU - $20
- Single core Sempron - $39
- Can't really argue with your choice of PSU - if you need a good one, you need a good one.
- Can't argue with the choice of motherboard.
With those changes, you'd save about $227. Of course, maybe that's pocket change for you, I don't know. But that's my suggestion.
Also, check out the link to the spreadsheet in my sig. It'll help you figure out how much money you can expect to make (or lose) by building a rig and mining with it. It's the Mine or Invest link.
Make sure the case is large enough to accept the VERY LONG VIDEO CARDS
Ventilation is also essential.