First, business class is not always ~10x coach. This summer, there were TATL tix for ~$2,000 return on CO, and somewhat more on NW & DL. For the best fare one needed to book 60 days out. These fares are often available at other times although not always as low.

Second, the strange pricing issue I run into is that on a TATL award ticket, the increment for WBC is 25,000 miles. If upgrading with miles from a paid coach ticket, the increment is 30,000 miles PLUS the $200-400 increase in upgradeable coach fare. With that difference, I typically book WBC over (so I can sleep) and coach back, hoping for an exit row on a 330.