Is there an ideal (ish) cartridge output?

what is the best output to give you the lowest noise without sacrificing performance. 
Higher output is definitely better, and would be universal, except its not free. There are tradeoffs.  

There are only three ways of getting higher output: more coils, bigger magnets, or more powerful magnets. There's a few more little tricks but basically that's that. Expensive materials basically forces everyone to using the same stuff at the same price level, and so it then comes down to how much. How many coils, how big the magnets. 

Either way, all things being equal, higher output equals higher moving mass - equals less detailed tracking. This is why at the top of the game pretty much all the best MC carts have pretty low output. Its simply not possible to track as well with more moving mass as less.

This also explains why Strain Gauge works so well. With a fraction the moving mass but much greater output (not to mention no RIAA EQ required) its a technological no-brainer.

Yeah, I actually think the two most important specs in all of audio are cartridge output and speaker sensitivity. They are like two sides of the same coin. If the speakers put out at least 90 dB then finding a good amp is easy because just about anything will do. By the same token if the cartridge output is medium range around 0.5 or 0.6 mV or higher, something like that, then there's a huge number of phono stages that will work just fine. 

I'm not saying there's not more to it. Simplifying, obviously. Those low output carts tend to have fewer coil windings which tends to lead to greater detail. But its all relative. The lower you go the harder it gets to find a phono stage that doesn't lose in noise what you gained in the low output cartridge. 

I don't know that you need to go all the way to 1.5 - 2mV to get there. But then on the other hand I think there's a reason some prefer MM over MC and its probably got a lot to do with this output factor. 

As for why there aren't more of them, chalk it up to the incredible drive of so many audiophiles to make everything so much harder than it needs to be. I mean look, bi-amping, bi-wiring and all of that should have died out years ago. Low output MC gives guys the chance to spend endlessly on step-up transformers, of which there are literally hundreds. These things are so incredibly load specific they are near tailor made for the audiophile who wants to feel so cool he made something work nobody else could figure out. 

What they really need to figure out, when you get to a certain level, you can spend near infinitely on this stuff or for a fraction of the cost leapfrog the whole mess with a strain gauge. But that's another one for another day.