Spend against the current bottleneck
If runs end before extraction, buy survivability or a weapon improvement. If successful runs discard useful relics, increase carrying flexibility. If stock sells too slowly or cheaply, improve the shop side and collect better price evidence.
Use a reinvestment cycle
Reserve enough gold for the next necessary action, then invest the remainder in a change you can evaluate. Run, extract, sell, and compare the result with the previous loop. A universal upgrade order ignores player skill and unlock state; the best purchase removes the constraint currently wasting the most time or value.