I do hope that most people will not fall for simple marketing traps like stretch goals to increase their pledges on kickstarter campaigns, though the recent trend to offer stretch goals on pre-orders suggests that some people are indeed influenced easily into overspending.
Now the features from the stretch goals are nice, I just doubt that they are real incentive to pledge more, they are rather a tool to manage and incite expectations for the game if certain budgets are reached. In other words, I hope that you can hype a game via it's stretch goals, but people will still not spend more to reach those stretch goals.
1. In my experience, actually most Pledgers are about Stretchgoals. Starbound as example, hat a lot of hate and so on due the Novakid Stretchgoals so they didn't add them earlier, and that even thought they are nice, not proper into the Lore/Story integrated. I won't claim all pledgers do that for the stretchgoals, i think alot do it to support the Game or to get the Boni which they offer, but i tend to believe(due my experience) that a large group of players, the majority - do it as well for the Stretchgoals. And in case of Divinity Original Sin 2 i'm sure of it, because in case of Divinity Original Sin 2 - the reason for Kickstarter was for the Stretchgoals anyways...
2. I get where you coming from, because look at most of the Stretchgoals in most of Kickstarter-Project. Some might quite neat, but mostly they aren't implemented properly, due this Stretchgoals are often nice candys for People to support the Project, instead of Features which are really intended to. Like i mentioned, Starbound. However you can't deny, that DOS2 in this case are pretty different. Look at the Game-Master-Mode and look how well it is done. And look about the Hype around this Mode, even before they properly showed it.
And look at the rest of the Stretchgoals, this aren't small gimmicks, this are proper up to amazing Addtions. New Difficulty, 2 new Classes, Racial Skills, Undead Origins, Romance/Hate Feature, Hall of Echoes, Game-Master Mode. If you truthfully and objective look into this, this is pretty insane, because other Developers would have sold this as payed dlcs or make an full Addon out of it. Okay the Community payed for them as well, but still it seems this Stretchgoals wasn't candys for people to support them, but more over real Features, which are intended, however which needed the extra Financial Support to deliever them, thats why they've even gone Kickstarter....
