The other guys are pretty much on with their advice. Not a lot you can do to make remarkable performance improvements. If the 3 months you've been flying is your only experience and you're already bored, you must be a fast learner. Well experienced pilots can do some amazing flying with a lazy trainer. I assume you already made some non-structural changes like moving the CG back or increasing the control throws. If not, do that in small increments and best to get help from someone who knows what to expect with those type of changes.
The Superstar probably came with an OS 40 engine. You could bolt on a 46 for more zing and you will probably want at least a 46 for your next plane. The engine and radio stuff can easily be used in your 2nd. plane.