I think it's worth it. I run an in-plant, and we have a C3080 with the IQ. Yes, you can do a lot of what the IQ does without it, but I think it is a massive time-saver and is more accurate.
Here's how it has helped us...
Image centering on the sheet is great (and by great, I mean exact almost every time), meaning set up for post-process is easier, especially if you're using presets on a piece of equipment. Folded jobs look great as panel lines match up very well. We also run the SD-513 saddle stitcher, and pairing it with the IQ means multi-page spreads look great.
Calibration is quick and easy. If I want to run press adjustments (gamma, density, etc.), the IQ reads those and it will calibrate the default press profile in the same set of processes. Creating new output profiles is also easy, you just provide the settings and it will kick out and read the sheets. I can generate a profile in just a few minutes.
You can set it up to automatically run a front/back adjustment before a job, or during a job after each x-number of sheets. Or you can turn on auto monitoring, and it will read color and position of every sheet printed (and you can select either or both). If it detects a deviation (which you can set), it will stop the press and tell you to remove a number of sheets (the sheets it detected errors on).
Here is what it will not do: Front/back registration on long sheets, meaning anything over 19" (maybe it will do this with newer presses? Not sure). Spot color refinements - I still need to use the X-rite. Calibration using the "Calibrate" button in Command Workstation; we use Color Profiler Suite to calibrate. The last two are Fiery-specific, and are likely a non-issue if you're using the KM controller.