No, it won't save tube life and running a MM into a MC input, while it will work, is not a good idea.
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Not all MC phono stages will overload. I have talked to the designers of the Herron and JLTI phono stages. The Herron MC circuit will take 30mv without overloading. The JLTI MC circuit will take even higher voltages without overloading. So overloading is not be a problem with some phono stages.
Most MC phono stages seem to have 47k as one of their default loadings. The inability to adjust capacitance could be a problem, though you could probably solder a capacitor into the circuit without too much problem. Or you could just use a interconnect with high capacitance as your phono cable.
There are lots of solutions to the problem of using a MM cartridge with a MC phono stage. What would really be interesting to know is why Crockusbird's preamp is noisier at 1-2 o'clock than at 9-10 o'clock.