you can cycle heroes without spending gold by raiding and abandoning a valley repeatedly, which you will end up doing anyway hundreds if not thousands of times to get medals if you are on a newer (23+) server. If you feel you have too much gold or resource, build a second city and send it a bunch so it grows faster, put in a second academy so you can run 2 research at once, and keep your wall defenses and barracks building with any extra.