I'm not in a guild, but can see where your greeters are a great way to make people feel welcome. Since you have such a large group, what if you had specific areas for different skill levels. The "Pros" could float from area to area to offer tips and assistance. You could even have name badges with "Ask me about ...." (paper piecing, cutting tips, etc.) on them so everyone would know what a person's specialty is. Just some thoughts.