BC has played Virginia Tech 15 times with the first game coming in 1993. According to Phil Steele's records, we have officially been the underdog in every game since 2000.
I don't have point spread data beyond 2000, but if you look at game recaps from 1995 to 1999, you'll see that Virginia Tech entered each of those games with a higher ranking than BC. I would assume they were favored in all of those contests.
The last time I believe that BC was favored was 1994. It was Dan Henning's first home game...BC lost. Assuming that the very good 1993 team was also favored, that means BC has only been favored twice in 15 games.
Point spreads don't win games. They are merely a reflection of perspective (the betting public's and the oddsmakers'). I am glad to see it shifting in BC's favor.