In the higher profile models, like the CLP340, 360, etc. the enhancement should be more noticeable as more effort is put into those models. The CLP320 is really the entry level and, as is the case with most manufacturers, they will hold back on the early models. Still shocked though about the cheaper price on the CLP320 - doesn't quite make sense!
It could be that the retailer is just trying to generate interest and to attract business before enhancing the price again - it may be temporary offer! Typically, a trader will reduce the older models to get shot of them ASAP!
Generally, faults occur in the advanced controllers and arranger keyboards owing to the amount of software running on the keyboard itself. You don't get malfunctions in digital pianos or straight stage pianos. At the end of the day, it's your choice but I can't help but think that the cheaper 320 may be a better deal for you.