Perhaps they are old, but maybe they just need separating into smaller clumps. Have you tried growing new plants from cuttings?

The Salvia regla is not a clump but a woody shrub so it does not separate into slumps like you can with other salvias. I have grown from cuttings. I have other bushes started from cuttings. i was just wondering about these old bushes.

Have you tried vitamins/fertilizer? I have extremely poor soil and even though I have read that most Salvia (nonnative) do not need fertilizer, it's just not the case for my soil. Have you checked for insect pests like scale or checked to see if the roots are rotten?

Salvia regla Jame was collected on a roadside by a ravine with a steep slope and had perfect drainage. On the opposite was an apple orchard. I think the soil was a somewhat loamy clay.

Mine is limestone marl on a slope with some oak leaf dirt. Not fertile.I have added granite sand and compost.