To go back to the OP, an IR can be kept current on either SEP or MEP, however, a ME IR also confers SE IR privileges (provided a valid SEP rating is held) whereas the reverse does not apply (even if a MEP rating is held).
Unless I desperately needed a current ME IR I would probably revalidate the SE IR for 2 years and then do the required MEP refresher training (if necessary) and ME IR renewal every third year.
Saying that, it would probably work out cheaper to revalidate the ME IR every year, with alternate years on the Sim.
I suppose it all boils down to what you actually need the IR for and what you are actually flying on a regular basis.
Just my thoughts.
