Yes,
When dust accumulates beneath the rubber keypads, which granted it will take some time, the electical conductivity will decrease to some degree. The same holds true with some types of switches. The worst problem, though, is when dust accumulates on the leaflet contacts of 1/4-inch jacks and combines with cigarette smoke and humidity. Then it turns into a black, gooey mess than really causes problems. I had to deal with this with one of my fan-cooled amps. The air was drawn not only through the air intakes, but was also being pulled through the unused jack openings. At the end of three months of performing in a smoke-filled bar room, many of the channels would no longer function unless you wiggled the jack a bit after it was inserted. The amp head was still under warranty and sent back for repairs. The tech called and said the entire interior of the amp was covered with dust and goey cigarette tars. Covering you equipment just makes good sense--something like parking your car in a garrage.
Gary
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PSR-S950, TC Helicon Harmony-M, Digitech VR, Samson Q7, Sennheiser E855, Custom Console, and lots of other silly stuff!
K+E=W (Knowledge Plus Experience = Wisdom.)