Cards earn cash, and cash can support later auctions and luck upgrades. Protect an auction reserve, compare each visible upgrade cost with what it would remove from your next bidding budget, and never assume luck guarantees a rare card.
Income and luck reinforce each other, but the creator has not published card-by-card yields or a luck cost curve. Measure $/s as (cash after − cash before) ÷ seconds, record existing total income separately, then compare the visible upgrade price with your reserve and recovery time.