Most of the light strings I own came with a spare fuse and a few spare bulbs. The challenge is in finding those spares if and when needed. I do agree, however, that at such a low price, they really are disposable.
If I question a particular string for any reasn, I tend to throw it out. Given the price point, I have to assume that every part of the string is made as cheaply as possible and I'd rather not risk a fire than save a few bucks.
A couple of years ago I bought a bunch of strings of LED Christmas lights to go along the 200 foot fence in front of our house, thinking that this would be a one-time investment. Boy- was I ever wrong. The LED's didn't fail but the sockets did. All the lights got donated to the Thrift Store just after Christmas. During the after-Christmas sales last year I ended up buying some "commercial grade" LED lights that were permanently attached to the string (no connectors!) and had a 5 little volt switching supply for each string. They've been up since Thanksgiving, and so far there are no failures (knock on wood).
Is a full wave rectifier enough to remove the flicker? One could add a filter capacitor, or use a nice regulated laboratory supply. LEDs usually want a current regulated supply, though, and I don't know how they actually do it.
We have also really enjoyed our LED strings except that the X10 modules we use to time all the various trees and outdoor lights don't detect them and think they need to turn off - it took us a while to figure out it was the X10, not the LED strings. We had to return to old fashioned timers.
I finally made the switch this year to LED bulbs. I bought the EcoSmart brand from Home Depot. They are indoor/outdoor rated, flicker-free (I assume full-wave rectified), and the one-light-doesn't-take-out-the-whole-strand variety. I'm extremely pleased with them so far. They also seem to have thought out the connector a little better, as they utilize a pair of round female pins to accept the LED lead that's folded over against a plastic pin. I have found a few sloppy female contacts but they are definitely better than the traditional ones.
Sometimes it's the challenge fo fixing things yourself. Sometimes it's about saving money. I had two recent experiences. Of the car alarm, I chose to pay a small amount rather than spend house tracing wires.