I'd also add that Dream Theater are my favourite band bar none, and I don't even know if I'd want to see them perform any entire Dream Theater album start to finish. The albums they cover are doubtless more important, significant and acclaimed than Images and Words, but if I've chosen to come to a DT gig it's cos I place more value on their own music than I do on other bands'.
Course, it's a very, very easy fix to avoid it, given that they play an entire start-to-finish gig at the same venue the day before, so I'd never suggest that cos I don't like the second-night covers they should ditch them. It's a really neat thing, that a lot of people enjoy, and those nights do feel fairly special. If you buy the ticket, you know what you're getting into, and presumably you know you're the kind of person who might like that kind of thing. But an hour is a long time to be listening to some music by a band you might not even like.