Rigga,
you cannot judge the worth of a safety case from an experience of reading only bad ones.
As I have pointed out, the certification documents for all commercial transport aircraft contain one large safety case. The regulations define a risk matrix for single-point failures (although it is not called that; it is called a "relationship between probability and severity of effects" in Table 4-1 of Lloyd and Tye's Systematic Safety, CAA Publications, 1982). There is a systematic hazard analysis of every system on board and it is accompanied by a demonstration that the requirements of the risk matrix are satisfied.
Airworthiness certification is obviously very effective. Commercial air transports are amongst the most trustworthy artefacts subject to dangerous failures which have ever been built.
So much for your contention that safety cases are mostly rubbish.
PBL