After studying both Stirling and steam engines over the past decade I came to the same conclusion.
My thought was to build a more efficient steam engine. One thought to improve efficiency was to combine the expander and boiler so only one surface dissipated heat. Another direction I've been pursuing is a linear, in-line shunt valve, dual-piston, "crosshead" fluid engine configuration to remove flywheel, eccentric, valve rods, etc.. The mechanics received a patent a few years ago.
Not being an engineer, I'm looking for engineering assistance in developing a steam-based residential MCHP solar thermal system to replace heating furnaces in the Southwestern U.S. and similar environments.