I felt kind of the same way (as the OP) when I first opened up X2, I saw just one noticable difference in the UI (which was the click to/click near(?) option)
But as I started working with it, I began to really appreciate the new additions and changes. In fact I upgraded both Breverb and TH2 to the full versions, I would have liked to upgrade R-Mix, but there's no special upgrading price, and I think the X2 version is fine by itself.
But what really won me over totally was after watching the newly released Sonar X2 video. Before I watched the video I consider this a half an upgrade "X1.5" but after I watched the Cakewalk video, I totally agree that it truly is a full version upgrade:
Watch the video if you have any doubts:
http://www.youtube.com/watch?v=xw5z9BKWD-I - I LOVE Sonar X2 - the only thing that's missing (and this is relatively minor) is the ability to change color schemes and set up the colors how you like. But I can live with the dark grey.