speaker power question


I have two 8W 8ohm speakers in an old cabinet(pinball machine to be exact), one of which is not producing sound.

To be on the safe side I would prefer to replace both speakers simultaneously with a couple that may consume less power. Being a pinball machine, the sound does not need to be wildly stellar, just consistent.

I guess what I'm getting at is; what would be a safe range of power and impedance values for replacement 4" speakers? Do I have to find 8W 8ohm drivers, or will some rated lower on the scales work?