Maybe. If you have access to 61.5 then you could add them for $5/month. Your total HD bill would be $15 and you would be able to keep this setup at least for a while.
If you wait till after 2/1, then you would not be able to authorize your 811 to receive the $5 voom pak. Your only option would be to swap out your 811 for a 211/622 and then pay $20 for the newer HD pak.
So it is a judgement call on your part. If you have 61.5 access, don't care about espn2 HD, the other 5 voom channels, or the other new HD channels and want to save $5/month, go for it.