A patent issued 17 years ago is likely close to expiring.
When it comes to licensing an invention, the fact that the invention
cannot be protected by a patent probably does affect its marketability.
You could not offer a potential licensee any exclusivity.
That said your description does not rule out the possibility that
your invention is patentably distinct over that issued patent.
I agree that patent protection for this type of "invention" (I think of it more as a new product) does not affect marketability. My guess (only that) as to why the similar device I found a patent for has never shown up at WalMart is that the technology 20 years ago was too cumbersome to make it worthwhile.
That's changed. But reading the patent, it is sufficiently broad (some attorney did his job!) to INCLUDE a pretty fair description of what I have (by the by: as luck would have it I actually first concieved of this thing about the same time this patent was issued--not that that is worth anything on the bottom line), so the distinction, while present mostly by dint of technology, does not seem to me to be significant.
Some questions remaining:
1. what's the life of an original, non-renewed patent? I have information about it being 3 years, 5 years and "forever." Which is accurate?
2. What does it matter? I have no intentions of patenting this thing, and will rely instead upon first to market for my $$. I think it may be a product a manufacturer/marketer of such items might find attractive. If they do, I will let them worry about patenting it, and or the older patent. And yes, I know this seems to rub patent attorneys and other experts the wrong way, but there it is.
Best,
Mike