Morten,
I’m just wondering if it would be possible/practical/in-the-cards to make an amp with LDRs? 
Not something I've ever seriously considered and for good reason. Variable resistors (LDRs are voltage/current controlled variable resistors) are not something you see used in amp design. I suppose they could be used if your goal is to have adjustable gain but that's a feature looking for a problem to solve. If the purpose of an amp is to turn lower voltage signals into higher voltage signals then you need devices and architectures that can amplify (i.e. increase ) voltage. I don't see LDRs playing a leading role in amplification per se.
The one exception might be in an integrated amplifier but then you actually have an amp with its own built-in preamplifier/volume controller where LDRs could be used but then again that wouldn't strictly speaking be using LDRs in designing/implementing the amp proper.
