The best stuff to glue the wood is from 3-M, it's a double backed tape for molding, if it will hold on exterior moldings it will hold the wood to your dash. I re-did some loose pieces about a year ago and it's still solid. You can use more than one layer of tape if the center of the molding is recessed.
As for fish-eyes in the urethane it most likely was caused by silicone, "armorall" etc. you have to remove all traces of it and then throw away the rags before you sand.