Have you been suffering from the "typical" 5th air issues? They have had a lot of unhappy customers with the airs. There are other options for you, but...
The coils have been (in my experience of having a coil and several close friends riding at least one bike with the air) more reliable. Two years ago the 5th element was the only game in town (for less than $600+), but now there are other options that fit the Blur.
If you just "want" to replace it (no real need) then I would say save your money. If you have been having issues with your air shock and are tired of sending it in and having seals blow, shafts die or any other issues then change shocks, but don't lock yourself into only one other choice.
Anyway, not a direct answer, however hopefully helpful.
K.