You can´t give a general statement to spin recovery and power, it depends on so many effects that it is different for different types of airplane.
One effect is the gyroscopic pitching moment. If you are yawing, (and you wildly do it during a spin) the engine acting as a gyro is producing a pitching moment. Engine rotational direction is constant, so pitching moment direction depends on yawing direction. This means for a right turning engine and a right spin a nose up pitching moment. Having more engine rpm (which must not be confused with more power for variable pitch props) makes you spinning more flat, less engine rpm makes your spin steeper and therefor (generally speeking) more easy to recover. For a left spin it is the other way round. Having two engines with different rotating direction, the gyroscopic effect is compensated. This is also partially true for geared engines where the rotation direction of crankshaft and propeller are reversed (i.e. Rotax 912/914). The heavier and faster rotating crankshaft nearly compensates the lighter and slower turning prop with its much higher inertial radius.
The other effect is the propeller slipstream giving you more rudder and elevator authority, which generally helps you in recovering a spin, as long as the slipstram really reaches the empenage due to the high angle of attack (it might run just above the tail in a flat spin and for long fuselages), otherwise it can´t help.
So it depends on the special type of plane what happens, its the job uf the flight test team to determine all the effects during certification tests, the POH should hold all the informations needed for best recovery.
There is a very impresive educational film from the german luftwaffe, recorded in the late 30s, which shows all this effects in flight for different types op plane. At least 3 planes were lost during the film flight tests, so the film shows really interresting tests details, they really tried any possible trick during steep and flat spins.
I don´t know if it exists somewhere in the web or can be purchased somewhere.