There's not much you need bother doing to the venerable 4AFE... (or 7AFE if you got lucky and found an RV model) other than stick a set of headers and exhaust on, and a free-flowing air filter. That'll net you a few extra ponies and a nicer noise, but that's about it.
To extract the most enjoyment from (what is essentially) an unremarkable shopping trolley, the best thing you can spend money on is suspension/wheels/brakes/bushes.
Drop it 40mm on a quality spring/strut package
Upgrade the brakes (I'd find a set of front and rear discs from the Japanese 2 door models)
Replace the suspension bushes with TRD/Nolathane items
Bigger swaybars
16x7 wheels and quality tyres
Do all that, and you'll have a proper fun machine.
It won't outrun Silvias in a straight line, but you will be amazed how well it carves up corners.
Then when you get bored, swap in the 20V silver/blacktop engine from aforementioned Japanese models and giggle maniacally as you send the tacho needle off the clock right around to 9000rpm :)