Epic level characters fighting dragons as regular sorts of foes (even if the dragon has a million more hit dice and abilities, is prismatic and has eight heads) just doesn't have the thrill to me...
Epic level characters, to me, are for fighting armies and entire planes of existence turned inside out, or gods maybe.
Dragons are the CR 20 creature your gaming group spent the last 16 hours trying to get too... no charges left in anything, enough spells left to "maybe" throw a dispel past the dragons SR and remove his buffs... and even though everyone is 200% guaranteed to die because the beast knows exactly where they are and how they are going to come at it, the group refuses to turn back...
Of course, this is all just one person's opinion. But that's something I like to see...