Before I give my answer, let's think about what burning STEEM does. Plainly, it reduces the overall supply which increases the value of all the unburned STEEM. It also slightly increases the value of the STEEM yet to be created, since the inflation rate remains static regardless.
Because of these effects, I would not burn STEEM except for a small amount. The reason is that just reducing the supply does not fix problems on the blockchain such as the existence of faucet rings. Scammers will continue to exploit, whales will continue to destroy the rewards pool.
The ones who should be burning STEEM are massive whales like Steemit, Inc. and others. Our small bits of STEEM do not help much, unless initiatives similar to @null are created to incentivize the destruction. If a whale bid bot was created where the profits were burnt I would consider using it.
Well, yeah, but we all know that isn't going to happen.
Putting it that way I guess it's kind of silly to think a few raised thousands or hundreds would make a difference... sigh....