We owned a 2007 revo, it is a great boat. There are a couple other minor differences between the newer model also. The rudder up/down lever is an older design, but is usually sufficient. There is I believe an upgrade kit available for the newer up/down system, but we never bothered to upgrade (the old system worked fine).
Same with the mirage drive system, there is an upgrade available to upgrade the drives to V2, but again we never bothered, nothing wrong with the old design.
When looking at the boat verify that the mirage drive is in working order, though they can be repaired quite easily.
The Revo is not known for hull failures as much as some other models, but it is important to inspect the area at the front of the mirage pocket for cracks (most likely failure point).
Scratches on the bottom are normal on a used boat, not much you can do to prevent scratches with the soft hull, but excessive scratches or very deep scratches can be a problem (though deep scratches can be repaired by the dealer, or someone with experience in such repairs). A heavily scratched and worn boat has less value, a used revo in good condition is quite valuable. I would definately put it in the water and make sure it doesn't leak (close inspection of the entire hull is important). My advise to anyone buying a Hobie is to take care of it, they hold their value quite well.
If the mesh pockets are badly faded (mine were), replacements can be purchased from Austin Kayak online or any dealer.
We had the sailing kit and sailing rudder on ours, and loved to sail (always carried the sail with us)
Good luck you will enjoy the boat.