Actually, there aren't that many abandoned stations. There is the old Haymarket platform that anyone on the Green Line can see headed to or from North Station, along with the bit of the old Harvard station visible from the Red Line. Other than that, you have some old bits of Broadway still intact, but not too much else.

It is worth pointing out that if you ever find yourself on the wrong side of a station, cursing the fact there is no way to walk between the inbound and outbound sides, keep in mind there probably is a way across.

Boylston, Chinatown and Symphony are three stations that were built to allow you to walk from one platform to another without crossing over the tracks. The risks posed by homeless people and thugs have kept the tunnels sealed - and there might be some ADA issues that would prevent them from ever being opened now.

I would have liked the T to have reopened the pedestrian tunnel leading from the Public Garden into Arlington station as part of the renovations. With modern CCTV, use of the much larger tunnel on the Berkeley side is once again viable, so why not allow for all four sides of the Arlington/Boylston intersection to have access?