More watts or better power ?

Hello, I am currently running a PS Audio BHK Preamp, which has a tube input stage, to a Pass Labs XA25, Class A (50watts at 4 ohms) power Amp, into a pair of Sonus Faber Minima Amator II bookshelf speakers. My system sounds very good, and at 4ohms, I have 50 watts of power to my speakers, which is on the lower end of their rating.

What would be a better investment (most bang for the buck) into the system? Replace the XA25 with a higher watt amp (PS Audio BHK 250?), or spend the same money on a power conditioner (PS Audio Power Plant II?) Or upgrade the Minima Amator (which are sounding very good) to another set of speakers.

The system is in my bedroom, I have a very small house, hence the smaller Sonus Faber Speakers. I have beenplaying around with an SVS micro sub as well.

Other system parts, Clear Audio Concept/ Concept MC, Pass Labs XP15, Little Green Roon Server, Schitt Yiggi, and a Luxman MQ 88 Tube amp in rotation.

Appreciate your input
Mark O