I used to live near there and have been several times. The mill has one floor of Hockney paintings. The rest of the mill houses several retail outlets and an excellent diner. The village is worth a look round as well. If you don't manage to fill your day I would drive up to Shipley Glen and over Ilkley Moor and enjoy the scenery.
Ooh it's lovely at salts mill you could easily spend a few hours there. And your only a stones throw away from haworth where there's lots to do, Main Street/bronte parsonage museum etc or bingley with its lovely stores/cafe and 5rise locks and east riddlesden hall.. Lots to do in the area!