Most controllers in consumer equipment is mask programmed and cannot be changed. Devices that can be software updated can be programmed obviously, but unless you can get a datasheet and a the programming specifications (both how to make the program and how to burn it into the controller), you can't and most controllers will be in-house markd andmay even be specially developed chips.
So, in short, unless you find a device with a known controller (which is rare), you still need to buy a controller (and learn how to connect, program etc. it).
A well established controller with lots of support is very cheap these days.
When stripping consumer equipment, the things to go for (besides the mechanical components; screws, motors etc.) are power devices (transistors, diodes etc.), coils, capacitors, opto electronics (LEDs and such) and perhaps some wire - sometimes there'll be flash ram or similar worth stripping as well.
If you wanna save other components, better get a box to store those circuit boards in for later retrival of what you need - no sense in cleaning the boards right away.
For the semiconductors, you'll need datasheets to use them properly and you need to extract and store them an ESD safe way.
The enclosures may be reused as chassis components if you really wanna milk it.