The current situation with the wallet software is that if an account has 0.000 VESTS, but has some STEEM and/or SBD, it cannot perform any transaction. Even transfer_to_vesting fails with the reason:
10 assert_exception: Assert Exception
a.vesting_shares.amount > 0: only accounts with a positive vesting balance may transact
I think that it's reasonable (at least) to allow users to power up themselves in any cases :) or even perform any kind of transactions.
Yes, I have some STEEM and want to power up myself. What's the problem?