I dismiss a few dozen senior heroes a week. How about allowing use to have one extra hero per city and charge for creating a new hero seat in each city?
The charge to get a fourth seat in out primary city is so ridiculous that I doubt many people spring for it. I would be will willing to pay a fee to get a new hero seat in each of my extra cities. A fixed fee of $10 each would get you $150 dollars from players that would normally not spend a dime.
Since the code is already there for transferring heroes to the extra cities, all we need is the ability to buy the extra seats. Then my cities would be more than just farms and barracks. I am working on city 14 now and would be willing to shell out the cash for the hero seats, unless you made them ridiculously expensive, again.