I suppose the longevity marketing promise of these new oils can't be wrong...right?
Actually, there is nothing "new" about synthetic oil. Amsoil was the first to create it way back in the early 1970's. Even though they guarantee their top o' the line m/c synthetic to hold its spec for 25,000 miles, I would never ride that far in one year, or leave an oil change that long, even if I did. I'm comfortable doing my changes at 16,000 kms (10,000 mi.) or one year and it usually turns out to be once a year for me.
There can be no argument about the superiority of synthetic over dino. That has already been proven, not only by the industry, but to myself, by myself, when I switched from a dino hypoid oil in the rear drive to a synthetic hypoid oil, after noticing lots of extremely fine metal particles accumulated on the magnet in the drain bolt, the reason WHY the magnet was put there by Honda in the first place. Since switching the final drive case to synthetic, the magnet has no trace of metal at all.
Your old school method will get you by though, probably for as long as you ever keep any engines running, but it is still costing you more in the long run with multi changes per year. Most people here always seem to be looking to do repairs or servicing on the cheap - aftermarket brake pads, air and oil filters, etc. instead of the costlier and usually superior OEM parts, so it is surprising to find someone who will spend more money on inferior oils, without a sense of being economical.
As an afterthought, how about considering the environment as well? You could continue to use and dump 12 litres of oil every year or just 4 . . .