Kinross is awesome of you know how to flow. The bowl is the funnest thing ever to ride. And some good mini stuff too. (my local)
Carine is more a skating park but its still good with some boxes and pyramids, a good step up and an alright bowl.
Bayswater is fully sick, it has everything. Including a huge 12ft vert half.
Leederville is always packed out with skaters. It has 2 pretty fun bowls seperated by a street spine/roller type thing. And it also has a cool mini.
SUBI bowls, one of the best perth parks in my opinion, small but super duper fun. It has a nice street section. A 6ft and a 4ft bowl joined together by a super sweet spine and a hella fun roller/hip/tranny kinda thing.
Subi Half, pretty self explanitory... a half. It gets boring after about 15 minutes.
Bullcreek, small but pretty fun. Nice spine and extension to air. And fun lines that are pretty endless.
Belmont, a pretty dodgy area but a pretty good skatepark, with a good scootering scene. A huge 12 or so foot vert back quarter with a 10ft vert spine. Nice fly box kinda thing. and quarters all round.
There are a few other skateparks aswell but I cant remember them now and I probably havent ridden them.
As for the amount of scooter riders.. Perth is full of em. At almost every skatepark in perth there will be atleast one local scooter rider. The main skateparks that have the most scooter riders are Kinross, Bayswater, Belmont and a few others.