I would like to suggest a new hideout event that may happen every 3 or 4 months.
This event would allow you to select either glue or Zeronite and have a sliding scale. 1 donut would be 1% of your overall storage which means if you are completely empty in the resource than 100 donuts would provide max storage amount of that resource.
The sliding scale is to allow added a donut amount that you are willing to spend. Say you only wanted 23% or 23 donuts worth of Zeronite bought during this even as that would allow you to get the big upgrade that you want.
During the event you would only get to add a % once to Glue and once to Zeronite to avoid multiple maxing of resources during one event.
Have a donut sale at the same time for the people with little to no donuts ability to buy and participate. This would also allow the free to play players participation as they can save donuts for the specific event or use what little donuts they currently have as 3 or 4% of storage can also make a large difference but the free to play that saves up 50 donuts to 100 donuts can make large strides in their hideout upgrades.
HZ is nice enough to have many ways to earn donuts and we should have a few big things to spend those donuts on.