Create 2 or 3 exclusive adventures that can only be completed with a Veteran General, including as possible reward, a unique building or stonework. Something uber-desirable to persuade players into buying gems and supporting the developers. Consider the following:
A mystical stonework that, buffed once, increases the entire output of a random work group:
10% - Pinewood cutter
10% - Mason
08% - Fisherman
08% - Hunter
06% - Farm
06% - Mill
04% - Iron mine
04% - Stable
02% - Gold smelter
02% - Coinage
The 'Mystical Buff Stone' could be sold in Merchant (black market) at an inflated price, for those with deep pockets, but available to all others with a Veteran General via exclusive adventure.
· Alternatively, award the decorative Pirate ship to your home island, decreasing traveling time by half, or something fun, such as a cemetery that produces a zombie settler that roams your island