if i had the balls, i would fund my pinnacle account with $20,000 and bet every single time i see a + next to a line. i'd probably make a fortune.
I don't know how much you are joking but IMO you are on the right track. It's a bit more complicated than you state but there are certain situations where, whenever I see line of +200 or more, I bet it. No capping involved. Just place a unit on it and add up the profit at the end of the month.
It's a big part of how I make my living.
Some situations it doesn't work - like with ncaab moneylines it's a disaster - but there are baseball, boxing, tennis, NBA, NFL, ncaaf situations. It's still important to shop outside Pinny because, if you have enough books, you'll still find an even better line a lot of the time and that makes a huge difference. And it's not completely simple; sometimes you have to narrow it down a bit and, rather than just bet all the dogs on MLB alternate runlines, only look at those that are American League away dogs. That kind of thing. It's a good idea to do a lot of test bets on a spreadsheet before you start putting real money on it.
But in my experience, your simple idea has a lot of strength to it.