I went to my first Lolita Tea party over the summer and it was great :3
We played the " Price is Right " all of us were shown a picture of some Lolita item (many were Brand, from varying years ) Dresses, hair pieces, and such. and then we all wrote down what we thought the original price was. (wild guesses were allowed)
The person who guessed the closest I think it was within $20 or something won! We had a relatively small group so we sometimes had two winners something you might want to keep in mind. the prises were cute stationary packs. Random stickers and cute paper.
I'm thinking the hotel will be proving white table clothes for your event anyway, but purple and mint napkins would be cute. perhaps someone would want to make small flower arrangements with purple and green flowers/ ribbon
In your case since you are events staff anyway; you might want to reach out to your Fashion Show coordinators and artists alley attendees. Theres always at least one Lolita table at a Con. They may either want to help or provide prises or have ideas .
my last suggestion is go to youtube search for Lolita Tea party, i know I have seen at least 2 videos of other tea parties on there.
... And to answer that question "Yes I live here and have nothing better to do "
Next Convention: MAGFEST