Unless the corrosion is on one or both surfaces of the contact area it does no harm. This is true even of very low voltage/low current connections. Even dedicated cable cleaners do not go up on the roof periodically to clean the antenna down line or out to the wall to clean the cable entrance. Surely these cables and connectors are in the most hostile home environment. Likewise do you know anyone who treats the connections in their car?
To see this for your self, observing proper safety precautions, disconnect a receptacle or switch. Look at the exposed copper. Is it uniformly oxidized? Your doorbell and heater themastat are low voltage, milli-volts in the case of old thermostats, but corrosion is not often implicated when they don't work.
Again, short of significant erosion from exposure, even the world's worst designed connector, the RCA phono plug, is self cleaning in use, and ordinarily remains free of corrosion in the contact area.
There is a major exception however, contacts in potentiometers or older TV tuners, that may not be used for long periods or across the full range, can become both dirty and corroded. Cleaners can fix this. Relays and switches may also have this problem.
It isn't so much that cleaners don't work they do, or that protectants can't slow oxidation or deposit of airborn ick, but they they just are not needed most of the time.
I can though recommend one brand and that is ProGold
, not the DeoxIT® GOLD GxL, mentioned above, but the real ProGold. You can use any leftover for fishing reels and bike chains. I've used it for several years on my bike and it is a great product.