Oh the workbooks. We are in the same boat. DD has no interest in them. I've bought them and she will do them a few times but then she's bored with it and could care less.

Here are my feelings on the questions pondered:

Challenging them - There are many ways to skin a cat as they say (yuck) and workbooks are not the only way to challenge a child. Tune in to her likes and raise the bar. If she likes puzzles, get her a harder one to try. If she likes playing games, pull out the more advanced ones and see how she does. Every day lends itself to learning and challenges. Just taking a walk outside sets up opportunities. Take a walk with a book about birds and teach her how to look up the birds in the neighborhood. This is way more advanced then anything a workbook could offer.

Repetition of workbooks - Depending on the level of gifted your child is at, the idea of repetition can be the worst thing for them. Most HG+ kids need to hear about it once or twice and then they just have it.

Learning to sit down and do things: This is the one bonus to the workbooks, because they start to develop the 'classroom' environment and prepare the children for that, but let's be honest. She will get plenty of that in Kindergarten and Kindergarten is not all about sitting down. DD's school is academic and though she is in the 3 yr old class they do Kindergarten level work (but all in Spanish) so she has the similar set up of Kindergarten: activities and lessons at the table; circle time; art projects, etc. Right now they are learning about the solar system. I have noticed that DD is all about sitting at the table in the kitchen with pen and paper to write notes for different family members. Though she has always been a calm child and had a crazy attention span it is even more so now and I suspect it has to do with her school experience.

So basically ... I wouldn't worry about workbooks. Just remember you don't have the 'normal' child and you will be walking down a different path and this is totally fine.