Ok, here's a few things:
1. If you're at all inclined to DIY, but an STC-1000 temp controller. I just built one for my fridge, and it's awesome. The two batches I've done since are already looking and tasting better than anything I've done before.
2. RO water is perfect for all grain batches. I only use RO, but that's because I'm on a well, and the water profile is not all that great. Read the above links. Lots and lots of good info. But for me, I add 1 tsp or CaCl and 1 tsp of gypsum for my batches (mostly IPAs).
3. How is your cleaning and sanitation procedures? I find it odd that your beers have steadily declined since your first few... I replace any tubing that begins to show signs of age. Usually every few months if it's getting a lot of use. What kind of racking cane are you using? The plastic ones get stressed and scratched, the auto-siphons are impossible to really clean, and the stainless ones are easy to miss bits of funk in. Are you using a plastic fermentation bucket? Maybe it got scratched and there's some nasties hiding in there.
I had a couple of batches go south because of some older equipment that wouldn't get clean enough (even with star-san), and since then, I make sure everything is tip top.
Good luck!
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