Much will depend on the value of the car - it would be unwise to home service a car that's a valuable asset. Owners will go to recognised independent specialists because it maintains and sometimes even enhances the value. Every visit being logged in the history file.
But a 'regular' classic car - a mini, MGB, Stag, Morgan (!), 924 etc - would be great fun to fettle and wouldn't make any difference to the value. In fact some cars might even be more desirable for having been maintained by an enthusiast. Buying a cherished car that's been well maintained by a loving owner, could be a smart buy.
Unfortunately modern cars are impossible to work on - look under the bonnet of an Aero, or an F Type. I wouldn't know where to start.
I used to service my Z1100 motorbike - oil, filter, plugs. If memory serves (and my memory is appalling), the cam chain could be tightened and the tappets were bucket and shim arrangements. All of this I could do. Quite impressive. Hahahaha
