This is an old thread but I was searching around the site and thought I'd give it a bump.
I have done some home testing with speaker wire. Very long runs. I have a non-typical listening area. Even at long runs over 50 ft I could not tell the difference between 16 gauge speaker wire bought at Lowes and some recently aquired 12 gauge brand name wire. I got the new wire for a bargain and wanted a fatter wire since I do have long runs. Just for peace of mind. No noticeable improvement though.
As far as RCA interconnects, I do believe I did actually hear an improvement with mid hi-end brand connects. Keep in mind though, this was an upgrade from the absolute cheapest connects available. The ones that are often supplied with new audio gear. I know....that might faulter in a double blind test. But I heard what I heard and thats all that matters.
Now there is one thing that you usually don't read about when the battle of High dollar vs. Plain low dollar interconnects engauges. Just like good, well known audio gear, interconnects hold their value incredibly well, actually much better than amps, players etc. So if you do want to spend mega bucks on cables and get names that are highly sought in the hi-fi community, you can get most of your money back if they don't meet your expectations. Hi end cables will likely maintain a resale value that seldom goes under 70% of what you paid. Look at ebay and audiogon. That being said, I personnaly can't bring myself to paying many hundreds or thousands of dollars for them.
Oh, and ofcourse there is Monster Cable. I, like many others try to avoid buying anything from them do to their bullyish business practices, but I have to admit a couple things. The banana connectors (monster tip quicklock) are simply the best I have handled. I love them, sorry. Also the XPCI speaker wire in high or ultra grade is very well priced and does look better than some of the more expensive companies wire.