Just as a note, im not sure how much this will help you:
I had an older slim model PS3 that was having issues with all sorts of stuff. Any games with anything downloaded to them (patches, DLC, or just a downloadable game) would have terrible frame rate lag, the XMB was constantly lagging, everything took way longer than it was supposed to. So I ended up buying a new Super slim model PS3 and then a few months later, after transferring all my games, saves, etc to my new PS3, I replaced the hard drive in my old ps3.
My super slim is now collecting dust because ive been using my slim, which works like it just was unboxed now.
From what I have read from your problems, your hard drive is probably toast. Hard drives are usually the first thing to go with people who gameshare alot... heavy HDD usage, always downloading and deleting.
I would say, sometime in the near future before your HDD bites the dust entirely, deactivate all of your slots, replace your hard drive and then reactivate them all. I would bet that a hard drive replacement would fix all of your problems.