Originally Posted by 
Robert
				
			 
			You can polish a turd (saw it on myth busters) but once you are done you just have a shinny turd.
OP I am not calling the Yaris a turd just saying you can polish a turd.
Altiain advice is good advice, but it sounds like you are going to keep the Yaris and thats fine whatever you enjoy driving.
If you are on a budget I would put shocks way down on the list of mods to go faster.  Good shocks are a lot of money and cheap shocks are not any better then the OEM shocks.
Items to go faster at autocross.
1.  driver
2.  tires
3.  tires
4.  tires
5.  other