Yes, if the car's condition checks out I would definitely still consider it, because
1) original 05/6 Ford GT window stickers may still be available from Ford Show Parts
https://fordshowparts.com/collections/vehicles/products/m-0222-mer ,
2) car covers and bags are still available, just kinda costly, but not relative to the cost of a GT,
3) having both keys is good, not to mention the title! If it includes the OEM inflator / tow hook, that's good, too. Owner's manual is also still available, if this car doesn't have it. And the OEM battery charger is probably good to have (even though it's junk).
Also, GTs without those things don't seem to be selling for much less, if any, than cars with all of it; maybe it will matter more in the coming decades, dunno. I think buyers value mileage, condition, color and number of prior owners more than those items. It could be that buyers are unaware or just don't care. Or they buy it anyway knowing or hoping they're still available from other sources, or don't view the car as a collector so just don't care whether or not all the additional items are there. Probably other reasons, too.
But definitely do a PPI on it first, by a GT expert if possible. Some are willing to travel, and they can definitely help you avoid making a bad purchase. Maintenance records are certainly nice and probably help sell a car, but they kinda only convey what the car's condition "should" be. Good luck! Let us know how it goes!