I don't think anyone goes that far with spot starting. It's strictly seeing if the pitcher is facing either a bad team or a team they have always succeeded against and then how that pitcher has been faring recently and/or previously against that team.
For example, Moyer has been terrible so far but was worth spot starting because he faced Washington and he turned in a nice start.
I don't know the answer to this question, but I think it's an excellent one. Oddsmakers are renowned for having access to all sorts of information that we don't always see — who is umpiring the first game of a series, for example—so it might make sense that betting lines could reflect something useful. In addition, if betting lines move in accordance with how lots of people bet, there's something to be said for the Wisdom of Crowds.
I haven't seen any studies about the correlation between betting lines and starting pitcher wins, but I think it would make a fascinating one.
I think its a poor utility. I mean, just over the past couple of days(please note W-L only applies to the team, not the pitcher):
Millwood -154 Loser
Moyer -132 Winner
DeLaRosa -140 Loser
Marshall -134 Loser
Hughes -122 Loser
Maholm -130 Loser
Maine/Gallardo/Lester/Jackson/E. Santana all won as favorites but likely unavailable.
Wainwright/Scherzer/Garza/Greinke/ all lost and as big favorites.
Possible adds 1-5 as favorites.
Already owned 5-4 as favorites
Kuroda -174 Loser
Washburn -124 Loser
Hernandez -112 Loser
Blanton -117 Winner
Miller -112 Winner
Wellemeyer -113 Loser
Possible adds 2-4 as favorites.
Already owned 3-0 as favorites.
Oswalt/Joba/Gavin Floyd all won as favorites but I doubt they were available.
Small sample size of course but it does not seem off the top that adding favored pitchers means anything as far as streaming for wins. Love the topic though and I plan on posting for at least a week how each possible add pitcher fares as a favorite.
That should be an interesting survey you are undertaking. I think the main time someone might consider the betting lines are for spot starters and maybe some non-ace starters. That's what I've been taking a look at, but I haven't recorded the results. I can say in a general way I don't think it's been a particularly good indicator so far, but my sample size is very small. Mostly what I've looked for are the wire starters where the betting line has the team as a -140 favorite or better.
Sometimes I find waiver wire starters where the line is up to -160 for the game. (Like you found with Sonnanstine for todays game at -165. He's available in 39% of ESPN leagues. He's not a particularly good K pitcher though.)
I think everybody starts their aces regardless of matchups, but showing where aces lose (or get NDs because the team lost) could be useful if it shows the lines don't work even for them.
Another thing is I don't think the sportsbook lines reflect only what their experts might believe to be the actual odds of the team winning, because I think they alter the odds to attract bets to balance their books for every game. If I'm not mistaken, the sportsbooks don't particularly care who wins the game, they primarily care about balancing their books. They want the losers to equal the winners so that washes out and they break even on that, and then they collect the vig from both sides to make their money. As bigwords mentioned, this factor would reflect the "Wisdom of Crowds" however.
It should also be noted that the Total Run Line is just as, if not more, important than whether somebody is a favorite or not. It's not just the Money Line. It's the Money Line compared to what should be expected given opponent, track record, recent trends, home/road, etc. The same goes for the TRLs.