My story: After years of 'slow flushing', it became 'no flushing' and no amount of plunger helped. Called a friend with a mini-x to dig up the drain and found a collapsed section of 4" PVC. Quite possibly damaged during the backfill in 1980 when the basement wall was repaired. Just kept getting worse. Thirty feet of new pipe and a cleanout and it's been fine for 10-12 years.
Just my opinion: if your sewer doesn't have adequate 'fall', a 5 gallon bucket of water in the toilet bowl once or twice a week will help you more than you might imagine. Low volume/water saving toilets may not move the crap downstream well enough. Then again, I'm not a plumber.