Since you are new to Subarus, then it is probably a good thing you got a 2.5i. It is a good car to start off with for learning the handling characteristics of the Impreza platform before stepping up the power. Try checking out your local autocross events and try your hand at it for a while. It will improve your driving skills and give you a better idea as to how you would like to modify your car. Start off with some better tires and go from there. Don't put yourself in major debt by trading your car in right away. Just stick with what you've got for a few years and you will be glad you did.
Also, whomever is giving you advice on modifying your brand new car does not have your best interests in mind. Mod-friendly dealerships are few and far between. Even basics mods can lead to denied waranty claims and leave you stuck with costly repair bills.