If by power-up you mean powering up the 72 STEEM in your account to add to your SP, and you're not interested in selling it, then sure why not?

If by powering up you mean using the SBD you have to purchase STEEM, then I guess sure, right now the ratio SBD/STEEM seems pretty darn interesting.

But both choices really do depend on one assumption, which is that STEEM will survive the bear market and the price will not go lower than today and eventually recover to it's previous higher levels. That essentially is still a gamble/speculation, obviously, and carries risks.

That being said, I am neither powering up nor powering down currently. I don't have as much SP as you do though, so it is easier for me to be emotionally detached.

If I were in your case then I would likely wait with spending my SBD just a little bit, or perhaps start converting it to SP slowly in small increments (dollar-cost-averaging over the timespan of several weeks). Because there is still a very very big chance that the entire market is going to see another huge downturn and altcoins will suffer more than Bitcoin will. Staying in SBD , since it is more or less kept stable, should in theory be safer than in STEEM.