I've always seen DT's approach to songwriting and album structuring as being similar to Yes. I saw it right away when I first heard Images and Words, and when JP pointed it out on Five Years, it made perfect sense. While I don't think they sound anything alike (except for a few passages here and there), they have the same proclivity towards longer songs. They like the idea of indulging the instrumental side of things, making epics and mini-epics out of relatively simple songs.
Unfortunately, it has lately seemed to me that DT's longer songs are often "artificially" long. It's not really a ten-minute song; it's a five minute song with five minutes of instrumental literally stuck into it. Yes instrumentals seem to flow more naturally from the songs themselves. True, sometimes the sudden change is the whole point, but when they (DT) do that the majority of the time, I begin to wonder if they can really write an organic, longer-form song.
They've gotten better at it. "Octavarium" is amazing, and has great flow IMO. Some of the other later epics have pretty good flow. But overall, while I think it's great that DT is influenced by Yes and aspires to be like them, I don't think they've reached it yet. Yes instrumentals sound to me like musical adventures, and they usually represent a part of the story not told in the lyrics. DT instrumentals generally sound to me like four guys showing off their chops.