Yeah, if you keep an eye on your fuel economy and it starts to drop then you have a good idea that something may need attention, maybe replace air filter, spark plugs and if that doesn't help then it may be time for a tune-up.I did a mechanics course at the tech many years ago.
But - wouldn't touch my car today. Too complicated. I agree - oil, tyres, basic checks etc can still be done.
Water, air, engine checks etc should be done - many don't do this.