McIntosh C35 opinions?

I haven't owned a C35, but have owned the C31V and C37. The C31V is more similar to yours, and my own personal opinion was that I disliked the digital volume control, which was noisy, but everything else was ok. The C37 is a better unit, but rare too. It added electromagnetic switching, and a motorized volume control, which made noises too. I liked them because they were a simple design compared to other Mac pre's, especially the C33, which I have also owned.
The C33 has too much baggage to suit me, especially if you're not into vinyl. Do you really need a compander, record circuits, an extra 20 watt amplifier, etc? Your C35 is a better sounding unit, in my opinion. I still miss my C37 at times, and wish I'd never sold it. I have the newer stuff now, a C46 and C48, so there's no comparison with what you're talking about. Also a lot more bucks involved.
I also had a MC2155 many years ago, and a 2205 and 2255. But my favorite, and still current amp is the MC7200. That one's a great experience!
The reason you probably haven't seen many comments on your model is that I'm not sure how popular those 3 mntioned models were at the time. I also thought their retro looks were nice compared to what else Mac was offering at the same time.
Bottom line, if you're happy with what you have, stick with them. I doubt you'd find the C33 much to your liking, especially if you like a remote.

As far as the volume control noise I mentioned, I probably should've been a bit more specific. Your model and the C31V have the digital control and I could hear it "clicking" every time I raised or lowered the volume with the remote. That annoyed me.
The problem I have with many of the older Mac amps is that they have the autoformers, including your 2155, and to me the bass is not as tight as I would like it to be. I can't speak for the newer amps, because I found the 7200 so satisfying, I saw no need to look further. The 7200, as you may or may not know, is direct coupled and puts out 200 wpc @ 8 ohms/300 wpc @ 4 ohms. The sound is tight and not dull, clear highs and I see no reason to spend a lot of bucks on something that may not be as satisfying as what I have. 7200's can be had for anywhere from $1200-$1500. I added the 17.5" wide face to mine, with the newer tapered end caps, so it looks like the current models, and matches my preamps.