Hi,
I ride the Altona jumps occasionally. There are two areas with jumps.
Queen Street Reserve on Queen St. I haven't been there in a while, but last time I was there I recall it was after some serious rain and I was impressed with how they'd already been tidied up to perfect condition. They have a group of beginner, intermediate and advanced jumps, so you can work your skills up. It's council maintained.
The next lot are about 1km south of the Queen Street ones into the 40acres it backs onto. You'll have to ride with your eyes peeled to find them. They've got piles of serious doubles. I think it's just maintained by riders, but they've done some tidy work and there were some great jumps there.
As for JJ Holland Park in Kensington, I skate there, and I hear they've had approval for the jumps to be made and funding for the dirt and building/maintenance, but that was better than a year ago I herd that and last time I skated, which was probably a month or two at most, there was nothing rebuilt. The ones that have been there are more a fun circuit, but not much use for DJing.