Heheh, I like the MVP invasion idea, but we have to think about a prize to this, the candies is a good idea but if it is not stats and transformation candies what could it be?
Anyway this suggestion is not about MVP invasion, we could make an alternate topic about this.
Now on topic, About the more group activity, since I believe you are a guild leader, you could try the Elite quest, Moon and Sun aura quest, Frigg's king shield quest, it would be a lot of fun if everyone in your guild is geared with similar items at the same time, they could share builds and not just use the guild for WoE and GvG events, I consider a guild as a community of people that helps each other to reach a certain task, back in the days I enjoyed a lot making quest with my friends and guild mates. Plus the GM team, Scripters and Spriters will always be working on new stuff so the community have always something to do.