I can always come up with some excuses unless I have a REALLY good show.

Obviously I don't have room for both the C4 and the FI, so it's a matter of which one has the best playability (tracking & ease of use) on stage and has the sounds that may work for me.
I've slowly been integrating MIDI connectivity along the way, starting with the Timeline, moving on to a synth and then recently moving to the Dr. Scientist Atmosphere reverb. No longer do I have to place pedals next to each other to hit multiple switches at the same time or dance on a bunch mid-song.
I also understand the desire to work within a pedal ecosystem like SA can provide...but I'm definitely one for picking out the quirky oddball stuff for what it has that's different. Like, currently using a patch on the Atmosphere that has a verb with a ring-mod on the reverberation that's being keyed to a LFO set to a low BPM that has a randomized wave-form.
I've really come to enjoy that I can build patches with the ES-5 that features traditional effects pedals and also MIDI pedals so that with one button you can really shift soundscapes pretty drastically. While I don't expect the C4 will replace what I have on the board, I'll be interested to see. Also, I definitely have some odd-balls that aren't on my board for size reasons (T-16, OC-2, Matryoshka) that maybe I won't feel a loss for with the C4.