touching up that ground trace is not enough... you have to strip off the soldermask back to the good shiny copper, remove the bad section and add something like a copper braid to replace the cutoff bits... that ground is vital to preventing noise and minimizing glitches...
At the very least, polish up the bad areas of that ground strip and tin the entire length with a solid run of copper... use a piece of stripped stranded wire as your base to cross the bad part.
As far as the mess of orange wires on the back - they need to be redone as there's all sorts of 'gunk' left there - needs to be cleaned with alcohol and the replacement wiring should be done more cleanly, following the tracks as best you can and not running wires too close - certainly use the right size wires, not oversized ones.... otherwise, this is a poster version of how not to do it (to be honest)
Again, check those continuities, don't be surprised if you fine a bad one or two in spite of getting sound out of the synth...