Yes, an increase in primary Z will generally lower distortion, lower the output Z of the amp (increase damping factor), and the HF response might be just slightly lower, depending on the OPT. Higher order harmonics may raise their head a little, but if the design is good, this may not be a problem.

If the tubes are run class A, there won't be any increase in output tube life. IF the output tubes are run AB, life should be increased, but to what extent depends on the idle current, plate dissapation etc.

Hope this helps.