One millimeter of air is a good enough insulator. Besides, the replacement board will be 5mm above those tracks because of the socket. The interference may only come from neighboring tracks on the same board. But I hope I routed the board correctly.
I am by no means an expert but my gut says 1mm distance (whatever is in between) is not enough to prevent electro magnetic interference. Do you have a reference for that statement, just trying to understand really by no means trying to say you are wrong 
Almost assembled, still need the OPAMP and a pair of FMW1...
No, I am not going to sell the boards, but I will sell a few DIY kits to cover my costs for this project. If someone would want to assemble and sell the boards, we could come to an agreement.
I am in the final stage of debugging the board. I had to do a few patches (see the picture below). The board now works fine - video works perfectly (including S-Video), audio also works well, but there's a slight problem with cassette I/O because the HCT04 chip has different characteristics than the originally used 4069UB and needs a different set of resistors and capacitors. Reading works, but the amplification level is not enough and this sometimes causes Device I/O errors. Even hooking the unused part of LM358 didn't help. So, I am going to try the HC series of the HEX inverter and if that doesn't work either, I will use the original component. It's already on the way to me from China.
Just to illustrate the problem - here's the picture. The HCT logic behaves differently than the original 4069 chip, so the signal is not centered at 2.5v, has smaller amplitude and it's also cropped at the bottom. All attempts to fix this by playing around with resistor and capacitor values (as well as by using the OPAMP) failed so far. So, I am going to try the HC series next.
I've solved the problem with cassette I/O, one slight problem still remains with the OPAMP. The internal machine's noise is heard in the audio channel while the original board blocks it completely. But the good thing is that now my Panasonic A1F has the official S-Video output on the back. 
