Hello,
Responsible game designer wasn't able to keep up with project. We decided to take it over.
As first step in upcoming patch (most likely Saturday/Sunday) we will add Boost price scaled based on amounts of stars received (5 stars - 20% of price), and very probably enable Dragonfang Ridge for new system now or otherwise with next patch.
Later, we will try to find another solution to given issues based on scratched information and other ideas. Please note that it might as well include reverting/changing/adjusting Boost price any further if other, better solutions are found.
However it may take a while due to busy planned September and October in patches. But now it should be more splitted into regular patches so certain changes arrive faster.
Greetings