Remember that valve power and solid state power appear to be completely different beasties... In fact, I've got reasonably awkward speakers (big floorstanders, 89dB but 4 ohm nominal with a couple of dips to 3 ohms) and in my moderate sized room (18'x16'x11') the 8 watts of the Minimax drives everything beautifully and without any strain (to volume levels at which sustained listening would do my ears no good at all).

So, it's often a red-herring.  Don't discount an amp just based on a paper spec alone - in the same way you wouldn't buy a car without at least test driving a similar one...