I don't know much about XKs particularly but when I was looking, the 08 WKs had basically two 'new' features that seemed relevant to me. The 'soft touch' interior, which is less noticeable when buying a limited with all that fancy leather - like your Hemi commanders probably are, and standard heated side mirrors on the laredo. Again that should be std on a limited anyways.
I can't give you much else help, but I don't see why you really need to get an 08, though you might want to consider the lifetime powertrain as a selling point. You CAN get that same warranty (up to a maxcare lifetime) on your used 07s if mileage is not very high, but you will pay an extra 1500 to get the powertrain (which would be standard on a new 08).
Good luck with your purchase, I'm sure others will be able to help you out more than I can.
xsrdx, They probably didn't order any '08s since they still had leftover '07s on their lot.
As for the differences, they're mostly interior styling and styling changes. The HEMI engines are the same, along with the drivetrain and other mechanics. Inside, they'08s have the newer MyGIG A/V entertainment systems, restyled dash and gauge cluster, remote start and other small refinements. '08s DO NOT have HIDs, those are only available on the '09s. The '07s have the older dash layout and audio systems with or without navigation, so if you can live with those, then I'd go with the '07, especially if they're slashing the price to the point where they're competitive with the used vehicles on the market. You will get the lifetime powertrain warranty on the '07s as the warranty is based on date of sale (after 7/31/08), not vehicle model year.
For the money, go with the '07s unless you just have to have the MyGIG system.
After test driving today, unfortunately the 07's they have aren't optioned as well as I thought following review of literature, and primary driver (wife) was less than thrilled with driving position and cargo area vs. current GC.
And 07 upgraded stereo lacks AUX input for MP3/iPod.
I found out they do have 08's, just not on the lot as they are still trying to move the 07's. We looked at a pair of very nice 08 Overland's, but I am left with spouse who is less than enthusiastic...
So we'll keep driving WJ for now. Maybe 4th Gen Grand Cherokee will be better fit.