Given that members aged 60 and over would receive a TRIS tax-free, does the issue of whether there is any tax-free component have any relevance?

Yes, even for a pensioner aged 60 or over, the tax free component may still have some relevance.  More particularly, the tax free component will again become relevant on the death of the pensioner in the event that the benefit then becomes payable to a non-dependant, such as an adult child.  (I.e., the adult child, as a non-tax dependant, would receive the tax-free component tax free, whereas the taxable component would be subject to tax of 15%.)