Craig, I seems that the real improvement in the strain gauge cartridge is it's tracking performance. It more readily follows the groove with according to sources much less record wear. I would assume the term solid state means more accurate in this regard w/o tube or other colorations. As for what sounds better is a matter of taste, accurate is not always better.
As for stylus replacement it is important to note that unless you order your strain gauge with extra styli you have to send your cartridge back to Soundsmith as each stylus has to be matched to the cartridge. So, it is no different than a moving coil or Iron cartridge in that regard. I would order mine with one extra cartridge.