I agree with henry, parking is a great feature that could attract more users and extend the overall adoption of NuBits, anything around 1 or 2% per year should be our base semi-permanent interest rate.
When the need arise, like now, we can increase temporary the park rate significantly higher, in the order of 15% short term 1 month, 10% 3 months and so on (annualized).
I think keeping park rates to 0% is wasting a very useful attractive point to Nu.