I've never heard about a another Vidia Book, Random House the comapny that publishes the series just put up Lily In Full Bloom to come out in May of 2010
Personally I would LOVE to see a new Vidia book, because I like her so much more than Lily
There is a rumor that after Lily, either Rani or Terence will get a book
On a side note there are books unavailable in the U.S you have to buy them imported from other countries.
There's
Tinker Bell takes Charge
Rani and the Three Treasures
and Art Lessons by Bess