Yep, last year after March I dropped from Diamond to Silver (as I only had 11 stays in 2011).
I invoked my VA WP Diamond benefit immediately and the member card that eventually arrived shows a Diamond Expiry of March 2014.
I just got VA Gold but I'm very likely to go Plat in the next few months. I'm guessing that my best bet is to go HH Gold now then use my Plat benefit to go Diamond after April of 2014... does that maximize the value?