Wondershaper does work on WL-500g. At first glance I suspect the problem to be with the bandwith parameters you provide (1300 and 300).

Lets focus on the upload stream only because that one is the most import:
You basically tell Wondershaper that your connection can do 300 kbit/s continuously, but in theory your connection can only do 256 kbit/s and in real life this would be only 200 - 220 kbit/s. This means that the script is planning more data on you line than it can handle, rendering the script useless.

Therefore you will have to change the script parameters to -lets say-: 1000 kb/s down and 200 kb/s up. This does indeed mean that you somewhat reduce the maximum speed of the line but gain a better responsiveness.

You can change the 'bulk' stream to use all available bandwith when none of the higher priority streams aren't using it (there are examples on how to do this in this thread) to improve efficiency.

Bottom line is: Bandwith management is a tradeoff between raw throughput and smooth streaming.