Just bought a nitty gritty, hear no difference.

I once had a Record Doctor II and a Nitty Gritty 1.0, and I can tell you that the Record Doctor is definitely not as nice.

With the Record Doctor II and the Audio Advisor formula that comes with it, you have to clean each side of the record three (3) times. (Wet, use the brush, flip, vacuum completely dry, and repeat.) You will hear a difference on old, uncleaned LPs after that point. It was pretty obvious to me. If you don't, the problem will be elsewhere in the system.

Also, record cleaners will not reduce the record noise that comes from damaged records. If anything, they accentuate scratches. BUT, you get a lot more information out of the grooves across the board. This may be relevant to what you have been noticing.

This may not be your problem, but my recommendation to make sure lp's get as clean as possible is to scrub copiously with manual Disk Doctor pads first and THEN transfer to the RCM. The RCM is great at removing anything that's been loosened up, but I personally don't think it gets down into the grooves and disturbs hardened in dirt as completely as the Disk Doctor pads.

What is the difference between the record doctor II and the record doctor III ?

The Record Doctor III has a removable tray for the spent liquid.

I had the NG 1.1 and I used to use a Sound GUard mat to scrub the record on before the vacuum stage. I found that the Sound Guard mat held the record in place and allowed me to really bear down with the brush to lossen all that would come off. I did upgrade to the VPI 16.5 and can do that scrubbing on the platter now. But one more thing is I bought the Needle Doctor Scrubbing brushes too. I found those worked much better than the NG Brush.
Good Luck!