This is probably a very good approach for most folks with other interests.. it works for me. Most of us HSM types can see the usefulness of an accessory, or better quality part, for almost anything we use regularly.
A friend had an Ungar HotVac desoldering iron, and the only tips available for it were Ungar's own, which were internally threaded 3/8-24 and ~7/16" dia with a taper to the tip hole, made of steel (I suspect a leaded alloy) that weren't plated with copper then over-plated with nickel the way many are made. The tips didn't wear out, they just wouldn't accept solder after they developed a scale that has to be removed with SC silicon carbide sandpaper, and redrilled to clear the hole of the internal scale.
I could see that an adapter which would accept inexpensive, commonly available 1/8" diameter tips would be a great alternative to the thread-on expensive Ungar tips. Later, when I had my shop set up, I decided to see if those adapters would sell on eBay, even though the HotVac units were essentially obsolete. I made the adapters from 316 stainless with a setscrew for securing the inexpensive tips. I sold every one I listed, and was asked for more.
That wouldn't be a business in itself, but it's an example of product improvement that other folks see as a necessary upgrade/improvement.
I envision countless other pieces of hardware that would enhance performance, or enable a device to be more versatile, by a simple add-on accessory.
There are many folks with no machine skills that would appreciate someone making a quality piece of hardware that would be convenient to have.
I'd suggest forgetting about patents and billion dollar ideas, and focusing on numerous thousand-dollar ideas, or many hundreds-of-dollars ideas.. and more will present themselves as one works thru the process.
There are a lot of pieces of junk plastic hardware that would be worthwhile to make from brass, for example.
I'd exclude items with safety issues, and possibly create a warranty that is limited to only replacement the broken part. Making parts for professional, technical or serious-hobbiest types would likely eliminate many average-consumer complaints, such as.. I can't figure out how to use the gizmo, or my child or pet was injured by your product (that they found on the floor).