[flaviut]

spicyjpeg basically described the sort of thing I was thinking of, but even for more boring things like opamps or transistors, it's a big hassle to track down or design a simulation model.

There's a semi-standardized file format for simulation models, but there are still differences between simulators. And every manufacturer's website is a different kind of poorly-organized, so it's hard to even find the models.

The other thing is things where high frequencies exist, like switching regulators. It's possible to simulate them, but there's all sorts of parasitics (imperfections from the circuit being made out of real stuff rather than lines on paper) that impact the circuit. I've only used KiCad, so I don't know if the commercial software here can model these parasitics, but they can have a big on performance.

[RF_Savage]

Things like pspice and microcap can simulate a lot. But if theres high speed digital and switchers on the board, simulating it all could take tens of hours, if not more.