Consider the following examples:

The work is mostly Kim's.
Only Kim resigned.

A question some of us had (e.g. here and here) was, aren't these examples of adverbs modifying nouns (which they are not supposed to do)? Isn't mostly modifying Kim's, and isn't only modifying Kim?

In both cases, the accepted answer is this: in these examples, Kim and Kim's are not simply nouns. They are nouns, of course, but in addition to being nouns, they are also entire noun phrases (NPs). And adverbs may modify NPs.

I somehow didn't like this answer, for the following reason: it seemed to me to open a Pandora's box. After all, any noun can be the sole constituent of an NP. This analysis would imply a vast number of circumstances under which nouns may be modified by adverbs---potentially, all circumstances in which a noun is the sole constituent of an NP. What then remains of our analysis of adverbs as those words one of the key characteristics of which is that they don't modify nouns?

I got the following answer, from Greg Lee: "The NP answer is correct. Your objections to it are no good. The Pandora's box argument doesn't make sense---just because an adverb immediately precedes a noun and there is nothing else in the NP, this doesn't mean the adverb modifies the noun. That is what your argument assumes, and it is just not so. In such cases, the adverb modifies only the NP and not the noun."

I do believe this is the correct answer. The problem is, I just don't quite get it.

Let me try to sharpen my question. Consider the following two sentences:

1. Adverbs never modify nouns; they may, however, modify NPs, even when the NP consists of a single noun.

2. Adverbs may modify nouns, but only when the noun is the sole constituent of an NP.

As far as I understand, the difference between 1. and 2. is no mere semantics. Could anyone clarify? For instance, could anyone give an example where 2. would make a wrong prediction (about whether some sentence is grammatical) but 1. would not?

Consider the following examples:

The work is mostly Kim's.
Only Kim resigned.

A question some of us had (e.g. here and here) was, aren't these examples of adverbs modifying nouns (which they are not supposed to do)? Isn't mostly modifying Kim's, and isn't only modifying Kim?

In both cases, the accepted answer is this: in these examples, Kim and Kim's are not simply nouns. They are nouns, of course, but in addition to being nouns, they are also entire noun phrases (NPs). And adverbs may modify NPs.

I somehow didn't like this answer, for the following reason: it seemed to me to open a Pandora's box. After all, any noun can be the sole constituent of an NP. This analysis would imply a vast number of circumstances under which nouns may be modified by adverbs---potentially, all circumstances in which a noun is the sole constituent of an NP. What then remains of our analysis of adverbs as those words one of the key characteristics of which is that they don't modify nouns?

I got the following answer, from Greg Lee: "The NP answer is correct. Your objections to it are no good. The Pandora's box argument doesn't make sense---just because an adverb immediately precedes a noun and there is nothing else in the NP, this doesn't mean the adverb modifies the noun. That is what your argument assumes, and it is just not so. In such cases, the adverb modifies only the NP and not the noun."

I do believe this is the correct answer. The problem is, I just don't quite get it.

Let me try to sharpen my question. Consider the following two sentences:

1. Adverbs never modify nouns; they may, however, modify NPs, even when the NP consists of a single noun.

2. Adverbs may modify nouns, but only when the noun is the sole constituent of an NP.

As far as I understand, the difference between 1. and 2. is no mere semantics. Could anyone clarify? For instance, could anyone give an example where 2. would make a wrong prediction (about whether some sentence is grammatical) but 1. would not?