Is there really ANY way to practice effectively in Melee if you lack opponents?  I know beating up on CPUs is generally a bad idea, but is there anything else to do when there's no human opponents if you want to maintain your skill level (or advance it)?

i dnt no

The best I hear is to practice techniques in training mode( combos on standing targets, CGs on avoiding, etc.) I usually play with CPUs but that's just me, and I'm starting to do the other method too.

stick to the basic so you wont be rusty,watch matches or techskill or even videos.keep up to date to see what people do when they play certain characters or watch match ups.that always helps on the long run.its always best to get out and play people though

oh yea and adventure is a quick fix as well

I practiced my accuracy in Target Tests, then I worked on the easy event matches, then I just started fighting level 5's, then I just worked my way up to level 9's, but it takes a while to master everything. So take your time.

Use lvl1 to work on ats.

I'd agree that practicing ATs against low-level CPUs or in Training Mode is the way to go.

I also should point out that virtually all my tech skill comes from playing competitively for high scores.

I've never heard anyone recommend playing in practice mode before ...
Not having the C-Stick is a nightmare for learning any of that gritty tech with characters like fox.
Why remove something from the game that might help you improve?

Though ... that said, there's only so much you can do by yourself.
Get really tech-happy, I guess. Level 1's have random spurts of DI. Use that.

You could practice chain throwing in training mode by setting the cpu to evade. Training mode will also help you find/practice true comboes.

Yes it does teach you true combos, fun ones like thunder to f-smash on fox or dair flacon punch as kirby and falcon.

I'm lovein your sig EPsilon933