In my experience. all the Rolleiflexes between the C and F series are comparable. By that time Rollei had the winding and focusing mechanisms down solid and were adding new toys... uh, features I guess is the marketing term. The two major changes were the removable hood and the coupled metering.
As I thought back to when I worked on a 3.5C last year and looked at my record shots, I lean towards me being wrong about these parts being plastic. One is a bushing that is under compression and is also used to establish the focus limits- you'd be a fool to make that out of 1950s plastic, and the Rollei guys may have been a bit silly at times but fools they were not. And the other piece establishes critical alignments for the focus knob and the meter block. Again, not a place to run a test on plastic.
If you are thinking of some of the cost-cutting measures on the Rolleiflex T, then no. The 3.5C is in line with Rollei's top cameras of the period.
'Mint' can mean sticking shutters and overall gumminess from old grease and such. Test it. The most important thing with this whole range of Rolleiflexes is condition, much more important than model name. They were all about as good as it ever got.