Different word-order shouldn't matter: Tibi placent gemmae meae novae?
(Or maybe it's the lack of the -ne !?) I was imagining a 'rising intonation' to carry the question, here.
Yes, it's the lack of the -ne, the guilty.
We don't know how they rose intonation for questions. They probably did. But in their texts, without "?", without "." , without any mark for a question, the -ne, was, ipso facto, necessary.
Yes, except when they left out the -ne, because it was obvious (as in a whole string of questions, one after the other).
A whole string of questions is a different thing. It's not the case here.
Can't "meae" be implied ?
Yes, in context, the 'obvious' possessive can always be understood.