IMHO, there is no "fair value" for BTC, as it mostly depends on adoption. Halving or ETFs are only minor factors to the price compared to adoption.
The real question is: if one BTC is worth 30k$ with less than 100 million users, how much would it be with 1 billion users? I'm tempted to say a few hundred Ks, but for sure more than 100 k$.