i'm sorry i don't have any "stats" for betting for/against streaks...
but if i can offer some advice...
you have to handicap each game on its own merits, regardless of what "streaks" the teams are on.
it's not all that uncommon for a team to get a couple straight wins due to their opponents having a terrible bullpen and blowing the game late...couple that with a third game being won by maybe some unearned runs and there you go, a 3-game "winning streak"
it doesn't mean that team improved its pitching or batting stats, they just got a little lucky. over 162 games, that WILL happen, both FOR and AGAINST throughout the course of a season.
EACH game must be analyzed on its own merits. EACH team must be handicapped based on their current pitching, batting and defensive stats...not just on their recent W's and L's.
if a team has won 3 or 4 straight, but they've been pitching AND batting worse in those last 3 or 4 games than they were before...do you really think this warrants betting on them? just because they are technically in a "winning streak"???? do you see my point?