200 miles should be easy to get; for far under 180 euro. I'd say that if you plan carefully you should be able to find something under 100 euro.

Like posted above you will not go back to silver. As long as you fly at least one flight, you go down only one level - meaning from Plat to Gold. So you will have one year of Plat, one year of Gold.

Being plat does have some advantages, like free Economy Comfort seating. If you are planning to fly long-haul, being able to get free Economy Comfort may already save you more money than the 200 miles would cost.