I have a home business (not sewing or quilting) and have a separate policy to cover my business items. My basic homeowners policy would not cover any business related items.
However for sewing items, even if I were not "in business" with them, I would think it prudent to keep an updated inventory of your more valuable items.
That said, the "value" of sewing machines is not an investment. The 10k or 20k sewing machine depreciates just like a new car once it leaves the showroom. Once it is past the "everything" warranty period (1- 5 years) the value --as far as an insurance agent is concerned-- will be a small percentage of original price paid to dealer.
Sewing machines such as the very expensive TOL (10-20k) are a lot like desktop computers. There are frequent new technologies and what was TOL a year ago is soon eclipsed. If they have a higher stitch count (have been driven) they are worth less. They really are a lot like new vehicles.
Even so, some day I hope to own one, just for the joy of "driving" a TOL sewing machine for a few years before it breaks down. There is nothing wrong with that at all! But, to an insurance agent, a 5 year old TOL computerized embroidery or LA set up is a **depreciated asset** not an investment vehicle. They will value it as a used item--not replace it with the current year's model.
I know how emotionally attached we get to our machines, we love them! But the insurance agent does not count the emotional attachment to your machine when placing a **value** on them.