Wow, what a great list! Thank you. Let me respond one-by-one to each of your points.  and  Yes, I should be able to do this. I'll try to get to it in the coming weeks.  and  I'll need to investigate whether it is possible. Just curious -- what would be the use case for -? If you came to my site through /r/Flipping then I think I know the answer.  My options may be limited here. I try to squeeze in a lot of information into each search result while staying at least somewhat touch-friendly (although I admit my site does not work great on mobile yet). I can look into integrating UnicornSmasher information into my UI though, similar to how I link directly to FakeSpot, ReviewMeta and CamelCamelCamel. I have never heard about this tool before, but I checked it out and it sounds interesting.  Thank you for the NYT link! Yes, I noticed that some of the functionality I had for filtering and sorting by discount started to look a little off lately. I actually even had to hide some features from my site that I had there originally. I didn't know that Amazo n was going through this change, but it makes so much sense now! Looks like I will simply have to remove all functionality having to do with sorting and filtering by discount.  I actually experimented with this, but had limited success. I will keep trying to make it work though. Once again, thank you for all your input! Feel free to share a link to my site with your friends or online communities.
Just wanted to report that I implemented your suggestion #1 and #2 (in form of adding the ability to reverse sorting by number of reviews by clicking on the link again).
I also addressed the points you made in  and . After I read the NY Times article that you linked to in  I realized that it is time for me to remove all functionality that has to do with sorting and filtering by discount. Also, inspired by your suggestion in  I implemented the feature where you can include multiple department refinements in your filter. It seems that Amazon only give you the ability to do that as long as you stay under the same top-level department. It seems that currently this is as far as Amazon will allow me to go toward implementing your suggestion.
I just added another enhancement along the lines of what you were asking for in  - ability to exclude categories from search results. It is near the bottom of the filter panel.
Have you found a way to filter by item or shipping weight?
Unfortunately, I do not think it is possible.