I'm more a Bob Dylan fan but my partner favours Mark Knopfler. In consequence, I have attended many DS/NHB/MK concerts over the years from small venues to large arenas and from relatively small-scale festivals to huge stadia. And, of course, I have attended a large number of Dylan shows over the last 45 years. While I have no inside knowledge about how things will happen on the forthcoming MK/BD tour, few comments from my perspective may help.
1) Do not rely on Dylan fans all being older. While I (and other) Dylan fans are getting on in years, many are not. There is, indeed, currently a discussion on one of the many Dylan on-line fora about Dylan's young fans (say, 16 to 30 years of age) came into the fold
2) Do not expect Dylan fans to hold back before charging to the front of the stage. It is quite common at Dylan concerts for this to start the moment the house lights go down. I have been fortunate enough to get front row centre seats at quite a few Dylan shows and have had to be ready to lift up everything I've brought to the show and step sharply forward to the stage apron in order not to lose the advantage of a good position. It doesn't always happen but often enough. It won't be a problem at the GA standing venues, of course.
3) BD fans are as fanatical as any others - perhaps more so if the number of books on Dylan (there are several hundreds of them), bootleg albums (also several 100s), websites (dozens and dozens) and the like are anything to go by - but you will also find a fair amount of criticism, sometimes quite vehement, as well as travelling fans who you will see at a lot of different shows.
There are also, incidentally, two surviving print fanzines ("Isis" and "The Bridge") which will doubtless cover the tour in some detail.
4) Dylan and Knopfler shows are very different in character. Knopfler talks to the audience between songs (often the same jokes repeated) with showbiz-style comments; Dylan does not. Knopfler introduces his band, usually with great generosity; Dylan does not. Knopfler sticks to a pretty similar set list each night; Dylan does not. Knopfler has a well drilled band and builds upon this in performance; Dylan has rehearsed many songs but is just as likely to change things unexpectedly in performance, living for the moment, as it were. The overall effect: Knopfler offers a smooth show with moments of great artistry but pretty much as expected night by night; Dylan offers greater variation both within a concert and between concerts, so enjoy the times when he really gets inside songs and delivers them with passion and authority.
5) Although some of the shows most beloved by his fans took place in the 1960s and the 1970s, Dylan has been playing 100 shows a year for the last 25 years. He also turned 70 this year. The effect on his voice is marked but, despite his now limited range, effective singing is not only about hitting the notes. Indeed, it is often the gaps between the words, the stress (or lack of it) on particular words and the stretching (or the opposite - compressing) particular words or parts of the lyric that really make the difference. His vocal delivery nowadays can also see him swallowing lyrics, so you'll really have to concentrate to get the most out of it. It's not always an easy listening experience and can be challenging but also very rewarding.
I emphasize that all this may change and may be redundant by the time the tour starts, as Dylan himself changes. He certainly doesn't need to tour as much as he does from the financial point of view but it's what he does and what he has been doing for 50 years now.