You sure it was the CV joint making the noise? They tend to click repeatedly when you're turning in the parking lot; ball joints are what tend to pop.
Not a MAJOR thing to change out in either case, but getting that shaft nut off the end does take a mighty big socket and a helluva lotta torque (a length of steel pipe slipped over a beefy breaker bar usually works). Changing out the ball joints takes a ball joint press, which you can rent from places like Autozone (free, but there's a $100 refundable deposit), unless they use the bolt-in kind on those cars - again, not a big deal, just time-consuming and requiring a bit of muscle.
ZX2's get in the ballpark of mid-20's in city, and low- to mid-30's on the highway. Pretty reliable cars. Not a whole lot in the way of mods that I know of for those, other than the usuals:
1. Drop-in
K&N filter (or cone filter)
2. High-flow cat and low-restriction muffler (please, don't get a fart can!
)
3. Poly sway bar bushings
4. Centerforce or other performance clutch
5. Fresh fluids and a tune-up
6. Performance ECM/piggyback chip/reprogrammer (pretty sure they're available)
There might also be beefier motor mounts and such available, underdrive pullies, poly shift linkage bushings and/or performance shifters, and a few assorted odds n' ends, but the above five or six would be about the only things I'd really recommend. They're just sporty, reliable little economy cars, kind of like the second-gen Ford Probe - nothing outstanding, but fun and easy to drive, and they're not bad-lookin'.
You've already found out about the crappy stereo setup they have, so no need to go into that...