Well, I don't think that a sharp increase to $20 would be useful in a short time for HIVE blockchain. There would come up a lot of new users who would come just to earn some $ with their poor quality posts and probably plagiarism.
Moreover, a HIVE user needs HIVE token to power up to interact on HIVE blockchain. Therefore, I think the less price of HIVE would cause the more HIVE Power.
It is very useful. It will drop again in price, but it brings attention. When thousands of accounts are earning thousands for a few week, it attracts attention.
This happens now at any price :) Many people joined in late 2017/ early 2018 when Steem price was up. most left - some are now orcas and a couple whales.
I remember the price of Steem was $8-$9 and there are many people from my country. Now not like that despite the recent ups.