I notice a few items that seem to be quite worse than other less expensive items, such as the Popstar Jeans over Nylon Shorts. Are there hidden secrets for some items?

This is not so, because all store items have their RRP set based upon their stats

Then what makes the Popstar Jeans better than Nylon Shorts?

they were better, but after an update that changed item stats, they kinda suck 

Oh, I forgot about that! I didn't chance the RRP after I did that.

My fault I'll sort it out.

Oi... I was really wondering why the jeans costed more and sucked in comparison...