basic performance upgrades worth it?

[gr8gatzby]

bought a 2002 malibu(23k.mi) last week and i want to upgrade to quality parts. i am a shadetree mechanic at best, but i can do plugs, oil, brakes, etc...some questions for ya:

1)i would like to migrate the plugs, wiresets, and O2 sensor all over to NGK, i've heard that NGK is the best, but what do you folks think? is it worth it.

2)using full syn mobil 1 5w30 with Bosch filter.

3)cold air intakes are fairly inexpensive, although i have no intentions of turning this thing into a rice rocket i'd like to add some beef to the box. is a cold air intake worth it?

4)computer chip: can i mod the engine by swapping out the ECU? i've seen these chips on ebay for under $20 that claim to add 20hp. the sellers have superb feedback, but i find it hard to believe the product works that well for that cheap. can you folks recommend a good performance enhancing computer chip for the vehicle?

any and all help is greatly appreciated. this is my first chevy.