Remember, that for other people, it's most likely their first sniff of a fragrance you are wearing. Don't let the curse of knowledge fool you, ie. don't attribute your own experience and knowledge to other people. We often let this happen; I have noticed that after getting to enjoy a scent I didn't like at first, I'm more inclined to spray it a lot, forgetting that it's the first time for people around me.
First time I smelled for example Montale's ouds, I didn't think they smelled god per se, just kind of interesting. People around you aren't approaching fragrances with an open-minded curiosity like you are. To their nose, it's all about instinctive first reaction, which often is, that fragrances we have had to grow to love simply stinks. This is important when I'm considering how much I spray. It doesn't really matter how much I splash or spritz, say, Guerlain's Imperiale. Vintage Route du Vetiver then again, can be kind of harsh to a more inexperienced nose. It's not only about the strength of a fragrance, but also the way it smells.
My argument is, that sometimes curse of knowledge described above leads people to spray loads of fragrances that shouldn't be worn in such quantities around uneducated noses. This is obviously just one form of overapplying, but many of the others have been discussed a lot already. I came up with this idea, when I noticed I've started to wear certain scents a little bit more liberally. I think there might be some truth to this.
Noggs, you said spraying lightly is about personal insecurity or external pressure. It sometimes could be, but generally I disagree with the insecurity part. I think it's more about being considerate towards others than anything else; being self-conscious should not be mixed with insecurity. About external pressure, in a way it is just that, but it's the kind of external pressure one should respond to. Namely, by not harassing others with his fragrance.
What is too much also depends on a country. People here in Finland aren't that used to strong scents. This leads to me being self-conscious about my fragrance. This is, in my opinion, right kind of self-consciousness.
So, I'm a light sprayer. What about my own pleasure?, you ask. I ALWAYS spray my wrist or the back of my hand and sniff myself constantly, ending up looking like a pervert.