TheMadScientist - 9:07 pm on Nov 11, 2012 (gmt 0)
Yeah, like I said before, I personally wouldn't change it to a 404 for the reasons you're stating about the link weight and visitors ... I might actually change the redirect status to a 303 See Other and see how Google handles that if I was going to make any type of change.
I think you're right in your answer being for visitors and Google has had it correct until now, so obviously, the 302 is being recognized and 'counted' otherwise you'd be asking why the wrong page is showing in the results or something along those lines, which means in this situation a 301 will definitely not correct the issue, because the 'issue' is between the content of the original page and the content of the destination, not whether or not the redirect is being handled correctly.
And, I really can't see 'just throwing away' the page's links, history, etc. like a 404 or 410 will both do, especially when you have an 'essentially the same' product visitors will likely want to find, which may again change at a future date, so it sounds to me like the index where visitors can find whatever 'essentially the same product' you have at a given time is the right place to send them. (Ignoring search engine handling for half a second, and doing what they say, since they say to build your site for visitors rather than them, of course).
You having it right for visitors and the other reasons you state, plus Google having it right previously is why my initial response is to not change anything and let them deal with the soft 404 however they want ... Also, by changing it, you will not know if they change their handling back to whatever it was previously when they had it right and you were not receiving the 'soft 404' notice, so by changing it you could well be 'fixing' something that they may 'refix' on their end, and once you change it there's no way you'll know if they reverted or made another change in their handling of the issue that would cause the 'soft 404' notice/treatment to be removed.
Every time I think this one through and ask myself:
"What's the right thing for visitors?"
"Redirect to the index page."
Every other answer involves search engines and building a site for them, which is what they say not to do, so if search engines were totally out of the picture and I just had to worry about visitors, what I would do is what you're already doing ... I certainly wouldn't 404 or 410 the page if I'm thinking only about visitors (or even visitors and search engines), there's no way, so other than maybe trying the 303 redirect as a test I don't see myself changing anything in this specific situation.