Yeah, those solar yard lights are kind of bad at first, but can be made good. The AA batteries are cheap 600mAH, don't last very long on a charge.
The older ones I have use two batteries, I replace them with NiMH 1600+ mAH batteries, can stuff 4 AA in there. Then I can put a couple bright white Leds in place of the weak amber. Also runs a microcontroller pretty good. Programmed three for RGB color change, one for a 5 led chaser. Thinking about a flame effect and a few other things.
Got some newer ones cheap, with white LEDs and a single AA. Haven't messed with them yet, board is kind of confusing. The boost converter is interesting, but not sure if there is enough current for a microcontroller and LEDs.
If you can buy them for $3-5, why risk stealing them? I don't salvage much anymore. Most components are surface mount and house marked, so basically worthless. VCRs and computers are good for motors and gears, few other things.