I would love to see another couple seasons of this show. Luckily the entire series and both films are avail on Hulu, but it would be great to see what they're up to now.
For one thing, malls aren't anywhere near as popular as they were over ten years ago when the show first started.

Bit of a late reply but I thought I'd answer anyway!
No, there hasn't been a fifth series yet. Doesn't look particularly promising that there ever will be either.
However you may be pleased to learn that the Kath and Kim film (apparently called 'Kath and Kimderella') will be out in September this year. Don't suppose it'll be out here in the UK despite being a popular show! Suppose it might air on TV at some point though.
They've filmed the majority of it in Italy so that should be interesting! I'm really excited about it!