I don't use my 1974 twin cylinder 4 hp Johnson as a standby but as an auxiliary. I use it pretty much every time I go out. I prefer to dock and leave the dock under power rather than sail. At the beginning of the season I put 2 gallons in the tank and I just put in another gallon. I tuned it up about four years ago and last year put a carb kit in it. I sometimes don't use it for two weeks. Also, the summer season is short here so I don't use it for nine months. This summer it's been pretty much starting on the first pull, maybe second. If I'm not going to use it for a week or two, I always disconnect the gas hose and run all of the fuel out of the carburetor. I've had no problems with pump gas and stabilized two cycle oil. Even with stabilizer I don't use gas that's older than a month or two, though. I had a Johnson brand plastic gas tank which was pretty junky and the new price is about $110. I replaced it this year because the old one had a cracked part which would've cost more than buying a third-party tank. I got a Moeller for about half that price and it's a much nicer tank. I have pretty much have zero gas smell on board now. So, there is some maintenance but I do find it plenty reliable.
Of course, I'd rather be sailing than motoring (either gas or electric). However, having an auxiliary I find very liberating. I really enjoy light air sailing early in the morning when the lake is flat. I have no hesitation going out even if I think the wind may die. If it does, and the morning boat traffic on the lake has started I don't hesitate to start the motor and head home. For me, five or 10 minutes of motoring is not bad compared to waiting for the wind to come back. And besides, if I'm sitting there with no wind, I start thinking about breakfast and another coffee.