Ternary processing instead of Binary
Are there difficulties differentiating between 3 levels of signal?


That's more electronic than computer science (and the issue could be different with other technology). The 2 levels signals we use are generated by putting transistors in a saturation state(*). They behave like switches and the whole technology is driven to optimize this behavior(+). Even without considering that historical skew, generating an intermediate level at a fixed value is more difficult than using saturation, will consume more power (a big part of the power is currently consumed in the transition between saturating state, you will need to stay in that mode where power leaks a lot), reduce the resistance to noise (can be reduced by increasing the supply voltage and thus the power consumption) leading to reduced fabrication yield.

(*) Historically, there has been computer working with transistor in a non saturated state. There is a speed advantage to that. Power consumption (and needs for dissipation) killed the practice.

(+) Analog circuits are made with different processes which are deemed unsuitable for large digital circuits and even small one which don't need an analog part.