new page to already ranking keyword?!

hi guys,

how do you see the following? what would you do?

the main page (store) already ranks on top 3 for a money keyword. the money keyword logically consists of a keyword phrase, i.e. buy XXX.

and the keyword: XXX also already ranks on position 12. the page does not have much content.

can i create a subpage now:
domain.com/xxx and create a good skypscraper text for the keyword xxx?

or can this cause the moneykeyword to drop as well? and will google recognize it and make sure that this subpage now ranks even better for xxx (since much better valuable content was created)?

look forward very much to your opinions.

thank you very much.

I'm experimenting with both now.

@praetserge

Okay and do you have a result yet?

If it's already ranking just push it further.

You will only cannibalize yourself.

Okay but how do you mean that exactly? That the home page will rank and then also the subpage with the corresponding skyscraper article?

so what I your advice? Do it or not?