The 32 bit EFI firmware takes some of the value away from it.
Since Apple is no longer willing to support those systems (already a problem for graphics card updates, and will be in the near future for OS releases), it takes some of the value away from them (less attractive in the used system market for those that realize these issues exist).
They're still quite capable systems for Windows or Linux, just not much longer for OS X (assuming the latest version is desired). If a user can use an older copy (contains K32), its still fine as well (especially those with Quad core CPU's).
Dual core CPU models, not so much IMO, as what's spent in the used market can be put towards a much better system, such as an '08. Not that much more $$$ (assuming the seller isn't insane), but you end up with much more computer and the ability to retain it for longer.