He has really improved over the years, also thanks to Guardiola I think. Lots of people expected he was the typical English overhyped gold digger moving from Liverpool to City but he really proved people wrong.
You can register on the official website so that they notify you once tickets go on sale. But, it is possible that tickets will be totally sold out already to club members.
We are talking about Valverde though he is probably looking into signing a 30+ year old strong back up with experience in La Liga. Don't think we will sign him back to keep him, only to sell to a higher bidder.