What does the expansion symbol on the card being gold instead of the usual silver mean?
This is new. The gold cards are what are used for an easier scenario. take out the others (unless I have that backward - my core sets didn't have these as they were introduced later).
Also, I've noticed that the encounter cards for the 2nd through 6th adventure packs for Mirkwood don't show the card number next to the symbol like all the other encounter cards do. Makes it a tad annoying trying to make sure you have all the cards you're supposed to have for each encounter set. My Hunt for Gollum has the numbers (I.e. 1/29) as usual, but Carrock on thru Return don't have them. Is this normal?
It was added later for this very reason. So they can't go back and change what was already printed. Perhaps the next time they reprint them.