The demo car at the dealer had Brescias and DCC. It felt fine in Sport as far as I’m concerned - is that a good indicator?
That said, for £800 (which I’d add to the deposit rather than the monthlies) I might just grit my teeth and go for it. Put it this way, other than the money (which will soon be forgotten) I bet no one regrets buying DCC, but I bet a fair few regret NOT buying it. And it can’t be retro-fitted either.
Sport mode on a non-DCC car doesn't impact the damper rate, just the throttle response and steering. The suspension is fixed at a single damping rate for all modes if DCC isn't fitted, so if it felt fine to you, then that's a good sign that you would be able to live without DCC.
Having said that, your second point is very valid. DCC allows the driver to adjust the damper flow valve which in turn changes the damping properties, so you get lots of suspension options to set the car up how you want depending on your driving conditions. If you do lots of miles and/or want/need comfort, the DCC really is a great option. The difference between Comfort and Sport modes on mine is remarkable, especially on the terrible London roads, so I can just sit back and relax without having to worry about being juddered around by lumps, bumps, potholes etc.