I started this as a comment but it got too long, so I'll post it as an answer. Since you're talking about closing, I assume this is limited to question posts.
If the question basically doesn't belong here (for example, off-topic, ridiculously over-broad, or not constructive), I vote to close immediately.
If the question just lacks needed details, I leave a comment and revisit it in a day or two to see if it's been improved. If the OP hasn't returned and the question isn't answerable as is, I vote to close at that point.
Ambiguous questions are a different matter. It's a potential problem with any question, but especially Excel ones. People invest a lot of time developing answers to a misinterpreted question. I've seen poorly worded questions with numerous detailed answers, none of which addressed what the OP actually wanted to know.
If the question is ambiguous and likely to waste people's time responding incorrectly, I usually comment and vote to close immediately. But I check back over the next few days to see if it's been improved and retract the close vote if the problem's fixed.
The aspect of closing being seen by a new user as rude, and potentially repelling them, is largely related to the comments (or lack thereof). It isn't really an issue if there is a polite comment that explains the reason.