We have been on the Crown Prince twice and we are going on a Nile cruise again in February. It is hard to fault the boat; food is abundant, varied and good; staff are attentive and cheerful. On our last trip three years ago the boat was showing a bit of wear and tear but this is only a minor quibble. We are spending a second week in Luxor at the Sonesta St. George which is a fantastic hotel. It will be our 7th or 8th time winter trip to Luxor.
To answer your questions:
Alcoholic drinks are expensive, a beer was 40EL (about £4) and spirits 90EL for a local single or 120LE for a named spirit (best to buy on plane going out) tea and coffee are average in price. Temperatures in mid January are usually around 30 in the day (but with no humidity and feels just about perfect) it falls in the evening and you sometimes need a thin pullover. We have never needed mossie spray even when sitting out on deck of an evening. In the past the boat has been full but we have spoken to people who have been in 2011 who have found the boats only about 25% full. We were on the top passenger deck which was fine. In 2011 the visa was just under £10 each at Luxor airport so have a £20 note ready and you will get some local currency as change.
Some tips: a lot of stomach troubles are apparently caused by coming back to the boat hot and drinking ice cold water (you will be offered a tour of the boat - the kitchen is immaculate and only bottled water is used to wash salads), take some antiseptic gel and us this or wash your hands after handling money. Hassle can be reduced by not talking to them - just ignore them and keep walking. At the end of the trip you will probably be 'templed out' but I'm sure you will think it a superb weeks holiday.
Get in touch if you have any other questions.
Edited: 4:27 pm, January 01, 2012