Brian, I also contacted FF centre and was told that any existing domestic upgrades (those freebies I received as Gold) would be converted on a one for one basis.

I also asked if the tier credits presently in this year would be granted credit certificates. No go. From 15 Sept every 250 status credits will be given one upgrade certificate. Shame that no recognition is given to those you have been loyal THIS year.
Especially in lieu of the jump for FF BC awards to UK etc.

If up to 4 certificates can be converted than I will purchase some as you have done.
To be honest I didn't even know about purchasing the upgrades and if it only 5K points it is well worth it.