My take
Given that there's a 30" display in every apple store I've seen it in use enough times to feel comfortable with its performance (colors, brightness, etc).
It seems to me you've answered your own question. If the monitor is still too expensive, I can see why you would want to wait. But if you're simply waiting for the next-gen, why? You say you're satisfied with the current display when you've seen it in person. The quality of the display won't diminish just because a new display is introduced. Or is there some feature you need or really desire that's not available on the current 30"?
- A built-in camera? It's hard to believe someone would wait just for that.
- LED display? Affordable, mass-produced 30" LED panels don't exist yet so unless you're willing to wait until 2009 or 2010, I wouldn't hold your breath.
- DisplayPort or HDMI? Well, none of the current Macs offer HDMI support so you should also be prepared to change computers as well (if you own a Windows video card, different story).
- Built-in video scaler? Some of the new panels are coming with video scalers, making them more suitable for movie playback. This is up to you and how you intend to use the display.
Even the newer panels from other manufacturers aren't head-and-shoulders above the 30" cinema display so whatever improvement you might see in a new 30" cinema display will be incremental, not revolutionary. Even when you compare the LED vs. CFL displays on the Macbooks, it's not a knockout. And as I said, LED isn't coming to the 30" any time soon so LED technology shouldn't be part of your evaluation.
My personal experience: after working with 21" CRT monitor for ages, I finally decided to go LCD. I got a 30" because portrait-oriented images would have been smaller on the 23" cinema display than it was on my CRT monitor and I didn't want that. I am happy with the monitor.
"We plan to introduce our first Macs with LED backlight technology in 2007. Our ability to completely eliminate fluorescent lamps in all of our displays depends on how fast the LCD industry can transition to LED backlighting for larger displays." -steve jobs, macrumors
^ rememeber this statement last may? i wonder what happened...maybe the iPhone said "no steve! pay attention to me, ill make you more money!"
He said they'd START to introduce LED's in 2007, which Apple did. He then qualified it by noting it will take a while to go completely LED for bigger display sizes because of current technical limitations. What's so hard to understand?