re: "Bolster" - A large pillow stuffed with fluff
Indeed, a hot spring is more like a glacier than the surface environment of Utah is like the surface of Mars.
Surface conditions on Earth are to Mars as surface conditions of Venus are to the Earth.
Nevertheless, something is renewing methane in the atmosphere of Mars, and the apparent absence of hot springs (even relatively "hot" springs -- which on Mars might be "room temperature" springs) -- or any sign of active volcanism makes it difficult to argue that non-biologic processes are responsible.
Of course, a biological explanation is just as difficult. But not impossible.