Or by the Genesis effect. After all, it was supposed to transform targets into life-bearing worlds. If it encountered something as tiny as a space station or a starship, it would turn those into absurdly small miniature Earths, structures without any hope of remaining stable; quite possibly, the orange smear we see around the Genesis planet is what remains of the Federation space station, and what would have remained of the Enterprise
had not Spock decided to play circuit breaker for the warp engine.
Wouldn't the wave dissipate before it found the planet?
If so, Kirk would never have been at risk. Why would he need warp drive to escape a wave that dissipates at a distance shorter than the one he just crossed at impulse?
(Okay, it has to be argued that Kirk didn't even have impulse available when fleeing the detonation - that sorry limp we witness must be thrusters or somesuch at work!)
Of course, if the wave was of a quickly dissipating sort, it could never englobe the nebula and turn it into a planet. The ability to reach as far as Regula is there no matter how one looks at it, thus allowing for Regula as the preferable conversion target and leaving Mutara the less likely option.