To add to the suggestion about the guild wars- how about using gems to increase the availability of the number of friends' leader cards. I'll assume I can use a friend's leader card but when I get to the battle it is not available.
Also a suggestion to make the Guild War cards more than just trophies. Make it a useful card like a special HP card. I've been stuck since I only have one hp card and the gem purchase luck gods have not been kind to me in the past few months. I would definitely be refreshing and increasing my participation for a more useful card. So far the Tree of life and Lucifer/Archangel types are not as helpful.