I do not know about scientific studies (which does not mean much), but at least anecdotally I think the answer is a yes at least for people who are not trained/experienced in making exactly these kinds of decisions.
One thing I have heard anecdotally is that people often significantly increase the prize when deciding to build/buy a house/car/vacation because they "are already spending lots of money, so who cares about adding 1% to the prize here and there to get neat extras" and thus spend years/months/days of income on things which they would not have bought if they had treated this as a separate decision.
This is a bit different from the bird-charity example, but it seems very related to me in that our intuitions have trouble with keeping track of absolute size.
Would scope neglect only affect include the application on altruism? What about applications to project scope and budgeting?