Nile cruise aren't like the ritzy ships you see in the ocean. Maybe, it's OK for a 2-3 day run down from Luxor to Aswan.
From Cairo to Luxor, most Anglos take a night train. It's cheap and reliable. A cruise from Cairo is too expensive and not that great - you get to see more on the train.
If you want to hoof it like the old days (& romantic) and have some time, some take a sail boat with a villager for 1-3 days down the river and camp at night. Stars at night make for some nice memories and it's inexpensive.
I took a sail boat for a day and there was NO WIND. Was stuck in a time vortex with the heat.....ultimately had to take a water taxi to get the f*** out of dodge.
BTW, 10 Egypitian pounds will get you most anywhere in a taxi in Cairo. Don't overpay and don't sweat it if the first taxi denies your offer. 10 is the secret magic number for locals.
Go to tripadvisor.com for more opinion in the Egypt forums...