Which direction is best? Is it worth changing my entire trip to one or the other direction for the boat part of our trip?

I don't think it makes any difference if you're booking things in advance. I waited until I was in Luxor to book a boat because I had friends to advise me there and a known travel agent to do the booking at a good price. So I took the boat from Luxor to Aswan then train back to Luxor. I'd just compare what the boats you're looking at offer in each direction. For instance, on arrival in Aswan I had a guide to Philae to end the trip. I liked that. Some boats include excursions to sites north of Luxor so see if something you'd like in that regard is included, or one way but not the other. It can all vary from trip to trip, too. But that sort of detail aside, big picture it should make no difference.

That is so good to know. Thank you!