Hi Michael,
I also live in Melbourne about 12K from the CBD and have found my broadband light pollution filter really useful. I was able to get it very cheap second hand so I thought I'd give it a try, but honestly didn't expect too much.
It's a very cheap Seben (do note that this brand will make a lot of people cringe around here
) so I was cautious, but it actually gets pretty good reviews on some German astronomy forums and rightfully so.
In my 8" Newt, M42 has slightly more contrast and it's easier to spot the dust lanes. The Carina Neb is where this filter really shines - with my eyes fully adjusted I can actually see it as you'd expect in an astro photo.
I also found M8 to be easier to see. It also makes other nebs easier to spot.
It does destroy color (my particular filter makes things green), but you wouldn't expect to see much color with an 8" Newt anyway when doing visual.
Hope this helps!
Cheers,