Excitement deserves a seat at the table, not control of the budget.

Enthusiasm is valuable and should be listened to; it points at what you want and gives you the energy to pursue it. What it should not do is set the terms. Left in charge, excitement commits money you do not have, time you cannot spare, and promises that a calmer version of you would never make. Its judgment about scale is consistently poor.

Separate the two decisions: whether to do the thing, and how much to stake on it. Let excitement weigh in heavily on the first and not at all on the second. Decide the size when you are level, ideally on a different day, and hold to it when the enthusiasm returns.