I tried to respond to your PM, but it states that you do not accept PM's or something along that line.
In answer to your question, with your tour, I believe the only time you may need dressy clothes is while you are in Cairo, if you decide to go out somewhere nice for a meal.
Otherwise with a grassroots type tour, the focus is more on comfort & usability.
Remember to pack tops that cover your shoulders & no plunging necklines & that knees should be covered too. This goes for the male travellers too!!
Hope you have a wonderful time, wish I were going along with you. Don't forget to try the lemon juice.........very refreshing!! And I want to hear all about it when you arrive home again......please don't forget the pics either!!!
All the best..........Debbie