I won't fly Y for more than 8 hours/sector with a decent break between FINAL. You can just about manage this RTW, but it's painful.
As to paying for business/first, I have. The first time, at the time of booking, the cheapest Y I could get from UK to Australia was ~1600 pounds (quite late and over christmas). The best business deal I could find was Emirates at ~1900 - not a difficult decision (other than cancelling the trip).
When I moved from the UK to Australia, I checked all the deals I could find. Again Emirates came up with the best deal. This time 1st at just 50 pounds more than business (company were paying for the business fare, I paid the upgrade !)
Just back from Prague, and the business fare (Austrian) was less than double the economy fare needed for a fully flexible ticket. Ok, the company pays, but the difference is not always as big as it looks when comparing the airlines "list" for business and the cheapest (very restricted) Y available.