I was in the very same situation: I always wanted a thunderbolt screen, and waited, waited, waited, like forever, hoping for a thunderbolt 2 version or at least a version with usb 3 ports.
I had to change my PC screen, so obviously I didn't go for the thunderbolt there, but bought a really great fudjitsu 27" screen with non-glossy display. The screen is awesome, colors are great, I love it. I use it everyday for work.
But then, I got my hands on a $350 thunderbolt screen and I went for it. I figured, I've wanted that screen ever since it came out, so maybe it's stupid, but I'm buying it.
BUT in my case, the situation was very different. I was buying the screen because I had an iMac 21.5" with a busted screen and was going to use the thunderbolt as main display if I couldn't repair the screen (in the end, I wasn't able to repair the screen, so this solution will be chosen) or to use it with my macbook pro if I ended up repairing the iMac screen.
The iMac repair took forever because I was waiting on some parts and stuff, which means I've been using the screen on my macbook pro for two months now, everyday, and it's a DREAM. I simply love it. The interaction between the macbook pro and the thunderbolt is perfect, but it was made that way. A few months before I purchased the thunderbolt display, I gave up on my "one day apple will make a thunderbolt display with usb 3" dream and bought a belkin thunderbolt dock, so that I would have usb 3 on my macbook pro (late 2011, usb 2 on it). Good thing with the thunderbolt is that you can daisy chain the thunderbolt devices. And the displays. I actually picked up a thunderbolt display for a friend (I'm babysitting it, it's in a box at my place until he picks it up) and I had a bit of fun and chains them both, it was actually pretty awesome. I read you can chain up to 4 thunderbolt 27".
For me, what was good is that I could plug in the thunderbolt display in the macbook pro, plug in the belkin dock in the thunderbolt port on the thunderbolt display, and plug in my Cintiq 24HD, so that I can have both my cintiq and my thunderbolt display on my macbook pro at the same time (which is otherwise not possible).
So, for the reasons I listed above, the thunderbolt was a very good match for me.
Now, like others said, think about it: do you really need what the thunderbolt is offering? (thunderbolt port, usb 2 ports, ethernet port, all that you already have on your iMac) The color is amazing, I must say. I haven't taken the time to calibrate it yet because I wasn't sure where I was going to put it in the room, so no use calibrating it everytime I move it around, but I believe the result will be good. If you think the thunderbolt port at the back of the display will be of any use to you, then yeah, why not! It is a very good display.
I own 5 screens, all of them are completely different and intended for different purposes, and I love them all. I don't do any gaming, so I couldn't say anything about that, but I do some webdesign, some drawing, and a LOT of text reading (but not on the thunderbolt, it wouldn't be a good screen for that).
The guy I bought the Fudjitsu from owned a Thunderbolt, he was a professional photographer, we talked a bit when I went to pick up the screen, and I kind of expected him to talk trash about the screen, like "it's overpriced, colors are agressive, glossy screen is horrible", etc., the kind of things you read and hear everywhere. But surprisingly, not at all. He loved the Fudjitsu, had actually been using it for photography and editing, was selling it because he was now sharing a studio with another photographer and they didn't need a pile of screens, and he said that yeah, the thunderbolt was super expensive, but it was worth it, the colors were amazing, and it was really a very good screen.
Sorry for the very long comment, but now you have a detailed opinion of somebody a little bit biased but not too much, who is working on 4 other screens on a regular basis, and who asked herself the very same questions you are asking not so long ago
