Well, i will leave you to decide what to do with the motherboard, but if its decided you want to "Dispose of it" i will pay for it to be disposed of to Melbourne.. 
I suppose it all depends on how much its going to cost you to fix it up (if its able to be). The "Gunk" sits underneath the chips and they have to be removed to clean it up...
either Iso (Isopropyl) or Baking soda paste (with water) as it neutralizes the acidity. I personally like to just flood (Yes literally FLOOD) the area with ISO because of its evaporation rate.
As I recall I scrubbed the board with baking soda and an old toothbrush dipped in to isopropyl before I replaced the battery then wiped it all down with isopropyl wipes. This was probably 4-5 years ago and it ran fine for some time after that, but apparently the corrosion was still there and spreading. I've uploaded some pics of it along with photos of the other stuff.
Speaking of battery corrosion I tried to fire up the A1200 040 accelerator today only to find its battery has leaked everywhere and the card no longer works
Gruesome close up shots of the dead accelerator are also here;
http://picasaweb.google.com/amithlon/AmigaBitsNPieces#
