Performance Questions

[Thoughtful_One]

Hey, I had a few questions about a few simple performance upgrades other general questions about my 1992 240SX base. Before I begin, I just want to say that I like the complete stock look of the car. It reminds me of the late model Porsches, especially the 1984 944. I do however want to upgrade my car but I am on a budget. I also have experience in building things but it will take too much time. My first question is about a CAI. When ever I see modded cars they always have some type of name-brand intake but what about eBay ones. I found one with idential tubing and a K&N filter. How drastic will the results be and will my gas mileage go down? Also from other posts I heard that in long run perfo. may be hurt because the ECU will try to correct itself. I am not too sure about electronics. Another thing is that the only restrictive parts seem to be the appendages to the box and the slightly square tubing near the radiator. Why would I switch to aluminum if plastic may resist heat better? My second question about perf. is STB. This has come up before but the eBay ones look very similar to name-brand ones. I like the design of DC because they actually look beefy. I found a combo. of 3 (Front upper, rear upper, and rear lower) but I was concerned about the quality. I knew the 240 was ding-prone but GOD, it seems that where ever I go I get some type of ding somewhere. My driver side door also creaks during acceleration and hard turns. I figured that the STB would help. I also did a complete tune-up (O2 sensor, plugs, wires, cap, rotor, and FI cleaner) but I don't feel any different. Can anybody help me with these questions? Hopefully I will be able to post some pictures soon and see what you think.