If you are of a sensitive disposition, beware that Cairo is pretty much all slum and there are some unpleasant sights out there. The pollution is thick - both in the air and on the ground, and especially in the Nile and its canals.
The trip to Luxor from Safaga is even longer so take pillows if you can. You get a picnic box on all the trips (even though you get a proper lunch), so water/drink, nibbles etc. are to hand. This is a 3.5 hour drive EACH WAY - take books, iPod etc. as some of the landscape is boring. Luxor was great. Valley of the Kings is the pinnacle so if you don't do any other trips do this one. Karnak also amazing.