Hi Sarah,
MVD is offered as an extreme last resort over here because, well, it's invasive surgery. So I popped off and read up some US Hospital and Clinic sites and they ALL say the same. Candidates for MVD are those that do not get relief or control of TN from medication. Your TN is, thankfully, well managed - and I am very happy for you at this time.
However, it is the nature of TN that it does seem to get worse in most sufferers as the years pass, with attacks happening more frequently. Yet this could take years, and your meds might still give relief.
My opinion. If I was healthy and my TN/Parasthesia was controlled by meds and I was offered surgery NOW to control possible future pain, I would decline. I could always revisit my options should circumstances dictate. Alas, I do not have these options anyway.
Whatever you decide I hope you stay pain free with few attacks for as long as possible.

Dave.