I love Dream Theater as much as most here, but some of these responses are downright scary. Rush should open for Dream Theater? They should Co-Headline? They should alternate closing shows? FOR REALS?!
Disregarding the fact that Rush hasn't had an opening act since 1994, and disregarding the fact that there are bands bigger than Rush that would honored to open for them given their standing in the industry, and disregarding the fact that Rush is a legendary band, Rush is a bigger draw than Dream Theater by MANY MULTIPLES. Rush averages a good 3-4X in attendance over DT and they charge 2-3 X as much. An average Rush show in the US draws ~ 10k and grosses mid to high 6 figures (7 figures in major markets). Dream Theater draws and grosses a fraction of that. They're not in the same league. Dream Theater's biggest show draws less and grosses less than Rush's smallest show.
I love Dream Theater but for those who suggest that these 2 should Co-Headline or even that Rush should open for Dream Theater, I'd suggest a crash course in reality because you're really disassociated from it.