Maybe you can add an exchange market ship where your "cheaper" ores do not become completely useless.
Add some sort of conclusion/story after maybe 1000m. There was someone that went to 1200m in the comments above but most people quit after 1000m. Endings can include killing the bug queen, going through the core to the other side, or hallowing out the planets. Helps for sequels.
Allow your compound the ability to move to other parts of the city (like in the other Last Stand series).
Location - Building type; total lot size; indoor vs outdoor area
Different amount and types of zombie raids
Different dropoff amounts (ex near a lumber mill, more wood)
Different environments (different morale effects)
Each area has their own storyline quests
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Details: Verified fraud page or threat source"