well, i'm not en expert on the subject, but i don't think you can really take advantage of a ported lower intake manifold without something else to help more air come in. and, if you're feeling confident in yourself, porting is really something that can be done in your garage with a little time and elbow grease. i haven't personally done it, but a lot of guys on here have. a u-bend delete really helps exhaust flow but i don't think that's part of the resonator, idk i could be mistaken. and a powerlog (plog) is a replacement for the front exhaust manifold, not the rear. the front one tends to be really restrictive, and with a plog, usually a 3" downpipe is used along with it to really help flow.
honestly, if you're looking boost performance, a top swap would be the way to go. with a little shopping around, you can do this for under a grand. and because the L36 has higher compression, if it's done right and you're not knocking it'll be faster than a stock gtp.