Vista certification worthwhile?

I currently hold the MCDST (Windows XP) certification, which I achieved by passing 70-271 and 70-272.

As an MCDST, you can upgrade to the "Vista" version of MCDST (called MCTS: Windows Vista) by passing one exam, 70-621 "Upgrading Your MCDST Certification to MCITP Enterprise Support".

Given the negative general opinion on Windows Vista, the low rate of XP-to-Vista upgrades, and the release of Windows 7 by Q4 2009, is it worthwhile to achieve the MCTS Vista certification?

I am leaning towards "yes", because since Q1 2007, millions of PCs and laptops with Vista have been sold worldwide. Additionally, it seems like Vista and Windows 7 are going to be very similar, so chances are that what I learn about Vista will be totally or at least partially applicable to Windows 7.

Should I get Vista-certified this year, or wait and get Windows 7-certified next year? I do not think that my MCDST certification ever expires. What do you think? Thank you.