Quite+noun for emphasis or importance

Question

I found the following usage of quite in the Cambridge dictionary:

Quite + nouns
We can use quite + a/an before a noun to give it more emphasis or importance:

There was quite a crowd at the party.
It makes quite a difference when the wind isn’t blowing.

I don't understand what emphasis or importance quite has in above two sentences: does quite mean very or something else in those two sentences?

Again, what's the meanings of the following sentences with quite:

1.It's quite a big town. 2.It's quite an old castle. 3.The film was quite a success.

Answer 1

I think that this definition from the Oxford Dictionary gives a clear explanation:

quite a —— (also often ironic quite the ——)
Used to indicate that the specified person or thing is perceived as particularly notable, remarkable, or impressive.

Quite a party, isn’t it?
Quite the little horsewoman, aren’t you?

Quite a party! means that the party is notable, but you would have to be at the party to know what the speaker meant. It could mean that it's big, or lavish, or good fun... or that somebody has vomited in the swimming pool, the sofa is on fire and the neighbours have called the police.

It could also be ironic, for example at a party where there is the host, you, and three other people all "having fun", and everybody keeps sneaking a look at their watch to see whether they can decently leave yet. You say Quite a party... to one of the other guests and he replies with a resigned Hmmmmmm.....

Looking at your two sentences:

There was quite a crowd at the party.

This probably means that there was a remarkably large crowd at the party, but if the speaker was talking to somebody who was also at the party, or if the speaker went on to elaborate about what made the crowd so remarkable, it could mean almost anything. The only thing that's clear from this sentence is that the crowd was remarkable in some way.

It makes quite a difference when the wind isn’t blowing.

In this sentence, it simply means that there is a notable difference (of some sort) when the wind isn't blowing. Where I live, the wind can bring rain, sand, high humidity or bitter cold, depending on the time of year, and its absence can bring unbearable heat. Whatever the wind brings, this sentence says that the difference is remarkable in some way when the wind stops blowing.

Regarding the other sentences, 1 and 2 are very clear because there is an adjective explaining what makes the noun remarkable: we can simply attach the adverb remarkably to the adjective.

1. It's quite a big town. -> It's a remarkably big town
   
2. It's quite an old castle. -> It's a remarkably old castle

The third sentence has a different structure. There are several ways of rearranging it so that it can be explained:

3. It's quite a successful film -> It's a remarkably successful film.
4. The film was quite a success -> The film was remarkably successful
5. The film was quite a success -> The film was a remarkable success

Answer 2

Quite in this pattern means something large or special.

We had quite a wait.(It was long.)
That was quite a party. (It was great)
There was quite a crowd at the party.(There were really a lot of people)
It makes quite a difference (It is completely different. )

Answer 3

It usually mean very, and also can imply certainty. So it's sort of like saying that there was certainly a large crowd at the part, or that it certainly makes a large difference when the wind isn't blowing.