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301ing the old URLs to the new ones will pass the link equity that they had gained from external links. However this doesn't necessarily equate to the new pages having the same rankings: there are other factors that will influence that. For instance, if the new page had much better on page optimisation than the old one then it could rank better. Likewise if the structure of your site gave more (or less) prominence to a particular URL then that might influence how it ranks. The definitive answer you are looking for is "probably not". However I would say that the more accurate answer is "probably not, but there is not reason you couldn't not equal of better the other rankings, if you pay attention to the other factors in play".

I agree that the 301 redirect would be your best option as you can pass along not only users but the bots to the right page..  You may need to get a developer in to write some regular expressions to parse the incoming request and then automatically find the correct new URL.  I have worked on sites with a large number of pages and using some sort of automation is the only way to go. That said, if you simply want to kill the old URLs you can show the 404s or 410s.  As you mention, then you end up with a bunch of 404 errors in GWT.   I have been there too, it's like damned if you do, damned if you don't.  We had some URLs that were tracking URLs from an old site and we are now here a year later (been showing 410s for over a year on the old tracking URLs) they still show up in GWT as errors. We are trying a new solution for how to remove these URLs from the index without getting 404 errors.  We show a 200 and then we put up a minimal html page with the meta robots noindex tag. http://support.google.com/webmasters/bin/answer.py?hl=en&answer=93710 "When we see the noindex meta tag on a page, Google will completely drop the page from our search results, even if other pages link to it. " So, we allow Google to find the page, get a 200 (so no 404 errors), but then use the meta noindex tag to tell Google to remove it from the index and stop crawling the page. Remember, this is the "nuclear" option.  You only want to do this to remove the pages from the Google index.  Someone mentioned using GWT to remove URLs, but if I remember correctly, you only have so many pages you can do this with at a time. If you list the files within the robots.txt. Google will not spider the files, but then if you remove the page from robots.txt file, they will start to try spidering again.  I have seen Google come back a year later on URLs when I take them out of robots.  This is what happened to us and so we tried just showing the 410/404, but Google still keeps crawling.   We recently moved to this option with the 200/noindexmeta and it seems to be working. Good luck!

If you're not experiencing any serious problems and just want to prevent future issues, I'd probably use rel=prev/next here: http://googlewebmastercentral.blogspot.com/2011/09/pagination-with-relnext-and-relprev.html It was designed specifically for paginated content and won't block your link-juice flow to deeper pages. Google has in the past said you can canonical to the "View All", but don't canonical back to page one. I've heard mixed results on the "View All" technique. One thing, though - you currently have all these pages NOINDEX,FOLLOW'ed, so it's kind of a moot point. What you could do is just lift the NOINDEX on page 1 of results and keep it for pages 2+. That may be your least risky move at this point.

I would go for the nice product URL's with (sub)categories in it. That way users and search engines will understand your website better imho. You should of course think well about your website structure before you launch. If you do that well and you're quite sure you're doing the right thing you should be good. I'm very interested in why David chose the /product system. Did that give your better results in the SERPS?