Here are some things to consider for cheap, fairly easy, and effective mods:
Suspension and wheels:You've already got new struts, and there's no need to lower the car at your age. Keep your suspension. Get the front strut bar that rotorimp sells on this forum. Get some P11 G20 wheels (they also came on some late model 240SXs). They look like this:
I think you can probably put your existing tires on them, but you'll need to research that yourself.
Performance:5 speed manual transmission swap is probably the best performance upgrade for the money, especially if you do it yourself.
The KA24DE sucks for modification unless you are going turbo. For a bit more power for cheap, get an ebay intake w/ MAF adapter, Apexi 3" cone filter, and have an exhaust shop build you a mandrel-bent 2.5" exhaust with 22" resonator and muffler of your choice. You can put a header on if you want, too, but they can be pretty loud. With all of those, you will lose bottom end to gain top end.
Looks:Clear front turn signals and side markers from ebay, and paint the little gray grilles in the front black.
Xenon front lip:
zerothread/193033
Switch the god-awful stock front seats for front seats out of an 89-90 240SX.
Silvia trapezoidal trunk lock.
That's all I can think of.