Piggybacking on @Charlie MacPherson's comment, I think another way to analyze whether it's worth holding onto this property is to look at the demographics in your area. In Charlie's experience with the train extension in Scituate, he saw a decrease in home values. This makes sense to me in that I think the demographics in Scituate lean toward more established and older families looking for a peaceful living environment. In my experience, talks of train extension in Somerville (formerly referred to as "Slummerville")-- about a mile or so away from Boston proper, showed increases in price in the exact neighborhood the extension was being built. Further, more mixed-use condos went up in that area as well. My thinking here is that the demographic attracted to Somerville are younger professionals (DINKs or single person household) and they accept the noise as a given to having access to the train. Also, this demographic drive less as well.
All this said, look around your neighborhood. Do you see older established families or so called millennials moving in? Who are your current renters now? Do you see mixed use condos being built or retirement homes or single family homes? This will give you a sense of the demographic trends and you can decide whether this will increase the demand for your property or not when the train comes in. Also, most city economic dept. break down demographics by neighborhood so you might want to check into this-- usually available on city's website.