Just my thoughts:
I wouldn't buy the Chunk OS unless you really wanted all the other features. If you were buying it as another filter, I'd just get the 00Funk. Even still, I don't think those two filters are all that different sounding. Both are pretty tweakable and wet, but not "organic" sounding - at least to my ear.
The Prometheus is a lot of fun when using the stepped filter mode, but personally I didn't care for the actual sound of the filter. But try one, you may have a different view. It is somewhat different from the Grinder tone. Like the Meatball/Grinder etc it also takes a lot of knob twiddling.
I also didn't like the WMD Fatman. Just didn't really care for it. It sounds awesome for the electronic sounds that John Davis uses it for, but outside of that it just sort of fell flat for me. But again, very tweakable and different strokes for different folks.
Some filters that I would consider different enough from the Grinder to make it worth it to have both would be:
MXR Bass Auto Q, Pigtronix EP-1, DOD FX25, Original Mu-Tron, Jacques Trinity and a few others that I can't recall at the moment. Maybe the new Robotalk 2 as well. I'll let you know when it shows up.