something like a C2 can really bring some excitment to the table... i highly reccomend trying it. I use it over the mix bus maybe 1/10th of the time and only put it on towards the very end of a mix and only tickle the meters...and for some tracks...it really just makes mix even better...and then for sub-buses, it's amazing.
i have never had good luck with distressors on the mix bus.
I'm sure the fatso is useful
i'm sure the hedd is useful
but i wouldn't want to spend that much money on something that I couldn't really have a lot of control and use for unless I had all the bread and butter covered
If you have descent converters, I wouldn't throw money on more, even if they are 10% better, until you have everything else covered...
If you don't have a highly versatile world class 2 channel comp in your arsenal, I would put that on the top...not just for level control, but tone shaping... and you may lose desire for "warming" devices...
Also, sorry to pry, ,but how is your monitoring. After I got good (midrange revealing) monitors, my life and mixes changed incredibly. I didn't think I needed to upgrade, because I knew people making great stuff and lots of money on Events, and Tannoys, KRKs, but when I did (from KRK V6s and MSP5s) my world changed. So your results may vary and the people I know probably just have more talent to find the midrange on those smiley monitors...
but I have absolutely no desire for any analog "warming" devices now, as it goes through enough stuff on the way in and on the mix.