The big place you'll want to gain is in the mid-range. Worth keeping in mind that "upper-end" in these motors starts in the low 4000s- if it's all stock that's where it's laying over.
If you're rebuilding the 318 upgrading from the 302s to something better would be a sound idea. The valve springs stock are basically all tailor fit to the what the OE engine was built for- few times will you change cams and not need to change the springs in any of the motors. A pretty much E48 style build with roller cam and some additional improvements would make a very good DD motor.
