I don't know that there is a fixed spending limit, or rule of thumb about such matters, and in fact, how much freedom the board has to make such decisions varies from building to building. Smaller coops tend to insist on consensus-building, while larger ones delegate this to the board; sometimes bylaws specify some of these details as well.
In any case, boards are accountable to the shareholders. So, if shareholders have concerns about the projects that are being undertaken, you certainly have a right to get in touch, express your concerns and ask for clarification on the priorities and financing -- and do so before making assumptions about their agenda. It may very well be the case that they have a good reason for undertaking some of these projects, even the cosmetic ones, that you just don't know. It's also legitimate to ask about financing and assessments.
Those are also questions to be discussed at shareholders meetings.