Katherine understands the importance of appearance. She knows that what she wears is seen as how she feels about her role as not just being a queen but how she feels about being Henry's queen and being The Queen of England.
No, her interests and values do not lie in jewels but in her beliefs, especially her religious beliefs. She also understands that wearing them shows that she understands the importance of showing Henry she values the jewels he gives her both as an individual and as his Queen while it also makes clear her standing to the others at court and tells the general public.
"The reader lives a 1000 lives before he dies. The [person] who never reads lives only one."
George R.R. Martin.