In my experience a CURRENT MEP rating will only be of any use to you if you are going for a job involving flying an MEP.
The fact you have had one shows you're capable, the fact it is not current only shows you don't currently need it.
When your log book is checked in the interview process and it is evident that the only MEP flight in over a year was a flight test, the question then could be "why has the candidate spent good money on something not required?", and will they continue such wastage if employed?
That said, if you're thinking of applying for jobs flying MEP's, then it will definately help to have it current. Bear in mind however, that most MEP ops will be single pilot, and thus will have comparitively high minimum hours requirements!
All the above is only my opinion based on personal experience.