I know the Accord is a family sedan, with 125 HP... What value (best bang for the buck) upgrades can I do?

I need a new exhaust system anyways, the OEM muffler fell off! And with tax refund coming soon, I am looking for whole system replacement/upgrade, headers & what not.

I think I should do the timing belt too, as I have about 218k miles and I don't know when the belt was replaced last, I just know it was replaced. Also the oil pan has a small leak, I lose about 1 qt every 3k when I do the oil change.

This winter I've noticed engine ticking/knocking in the cold mornings. Could this be the oil pump starting to go? I don't remember if it does that with full oil levels (small oil pan leak)

I am not looking to be a weekend Rice Racer, just abit more oomph