I think the overall idea is rightm, better (more upgraded) plots should be more attractive to work on. I would like to support that with following ideas.
Bonuses should depend on specific levels of specific buildings for specific missions and also non-linear, so that plot speciality could be concerned.
For example, for a default chance of 0.5% of findind a crate:
Power Plant L1: +0.05% chance improvement
L2: +0.1% chance and higher chance of getting rare
L3: +0.2% chance, higer chance of legendary, +0.05% chance for plot owner
This should incentivize upgrading to higher levels despite the higher costs of L2 and L3.
For this to be effectively meaningful, in future avis should have ability to filter out and select a plot they wish to work on by criteria as on NFTKey. For example I want to filter out plots with Power Stations at L3.