My Karate gi is pretty old and it was a middle-range one (not imported). I begin to be quite experienced and I'm thinking about buying a new gi. Do you really feel different when wearing a top quality japanese gi (the "clap" when you execute a technique, the overall comfort, the performance during a fight) ? I practice full contact karate at 170 lbs, and was thinking about buying a heavy one.
Yes, you can really feel the difference in a gi made of heavier weight material. I own a few heavy weight gi I purchased once I reached dan rankings in their respective arts, and they held up very well over years of hard use and many washings. The light weight gi can make a whip-cracking snap, but the heavier weight gi make a lower register whoosh and pop. My really heavy judo gi don't make much of a sound at all, and are still almost as stiff as a freshly starched BDU top. If you buy from a reputable source the higher cost balances out with the durability, since you should not need to replace your gi nearly as often (though YMMV).
A good quality gi has the advantage of good quality: comfort, durability, and aesthetics. Heavier gis are generally best, but may get very hot in summer.
Despite what so many say and practice, the sound a gi makes is entirely irrelevant. It is no sign at all that a technique is good or powerful, and concentration on this is rather a symptom of egotism and empty self-congratulation. It's similar to how, in Go Rin No Sho, Musashi describes some samurai as being conceited about their muscular forearms. It helps to train in a tracksuit or t-shirt to rid oneself of this.
Concentrate on relaxation, good form, being rooted, and disciplining your mind and body.