Both great questions. I believe vests ultimately affect everything that SP does, so your curation rewards, how quickly SP goes up from "interest", and the amount you add to a payout when you upvote. What I haven't figured out yet is if two people both have 5000 SP, do they always have the same # of Vests or could it be different depending on when they powered up, etc. That's something I'd like to look into more.
For powering down, yes I believe you would lose a small amount of vests if you reinvested half of the recently powered down Steem since the conversion rate would be higher. Might have to look into that more and see if there are any scenarios where that doesn't happen. Thanks, you have me thinking about a lot of new things now which is always good.
Glad I could help promote thought. :)
These could be really important in planning powering down priorities. If it's a factor, then it would also bring up the question as to which SP you're powering down? The stuff you bought two months ago or two weeks ago. Strategies would change in accordance, right?
Thanks for the quick and thoughtful response.