Rarely. Believe that if you're betting with reputable shops the number you're going to get if a pitching change occurs is going to be fair.
Not to mention I put in most of my plays (i.e. not scalps, 'capped plalys) shortly before first pitch 90%+ of the time so a pitching change that late is pretty uncommon. And in capping I deemphasize starting pitchers more than most; I tend to make my calls more based on the team and how each side has been playing, what I expect in the future; etc.
While I'd say most people probably weight starting pitching 50,60,70 percent of their calculation on a game I rarely count it more than 20-40 percent.