I'm in Dortmund and I can tell you the truth about the ice rink. I visited the NRW Trophy since it started in 2007. Until 2009 it was free to visit, then the first time they have made ticket prices but just 5 Euro a day, which I think is very fair. Actually, there were so far just very few real visitors, the 3 rows were mostly filled by skaters, coaches, friends and parents.
NOW just two Olympic Champions are on the entry list and everything changed and went crazy. I AM NOT going there just for these two but all of them. I like them all the same. I just got an ticket by very lucky circumstances. Because I never bothered about it, because NO ONE was really interested to watch it!
There are just about 150-200 seats, I never counted but there isn't more. This competition was never made for the big stars and large audience. It is the practice rink used for Worlds 2004. Besides this rink is another Eishockey rink, that is much larger, there can be about 5000 spectators. But it is impossible to move the competition to the other rink, because it is an ugly icehockey rink, that is open at the sides, so very cold.
So you should be able to see at least the practices, but I don't know how they organise it.
AND btw, this is a very small venue, so you can meet the skaters anytime anywhere, so it might be worth going there anyway ;)