If you own only Trust Club points then having any other timeshare will open up access in II to MVC weeks. There are much, much cheaper and better ways to get a trader for II, if that is what you want/need.
Having Sheraton flex opens you up to the inventory that is in Sheraton Flex portfolio and also in the VSN exchange, which is different to what is in II and what is in Abound.
If you find that having Sheraton Flex is something that you need, you'll find that it is available resale for free, so paying over $10k for it is not a good deal. Much better for accessing the VSN exchange is one of the "mandatory" resorts resale, like Westin Kierland, which might get you a lot more Star Options for the money.
The choice of an II trader or one for use in VSN is likely to be different, so its worth having some clarity on what your requirement is. 20,700Flex points aren't many, so you may find it a struggle to use them. Its a classic sales trap to sell something that appears cheap, but is close to useless, so people come back and complain and get told that they need to buy more to get access to more inventory.
Is there something that you feel is missing from your current portfolio that you want to be able to access?