"Stories are so much a part of our lives that many people seldom think about them." : The use of 'so' and 'so much' as intensifiers

Solution 1:

The phrase so much is modifying the noun phrase a part of x in these examples. It isn't modifying the verb BE. We most often see this pattern when adverbs like so, too or as are modifying an adjective which in turn modifies a noun phrase:

• so forceful a blow
• too convenient an excuse
• as brutal an attack

Notice that these adverbs can also modify the word much:

• He was too much a part of us, to let anything bad happen to him
• The lobbyists as much a part of the political system as the political parties themselves.

In the examples above they are being used with the noun phrase a part of X. However, we can use them with any noun phrase as appropriate:

• He's too much a gentleman to be a scholar.
• Fuseli's Macbeth is as much a hero as a villain.

Solution 2:

There's two totally different things going on there.

1)

"so much" is synonymous with "such", eg

"Law is so much a part of my life" = "Law is such a part of my life"

2)

Using "so" on it's own, as an intensifier (as in "I'm so marrying you!"), is a relatively modern informal (ie ungrammatical) usage, and is often used for comic effect, possibly because it is so ungrammatical.