If I'm interested in EMC precompliance testing (with both conducted and near-field probing), are the lower-specced analyzers around 1.5 Ghz capable for the job or is more range needed? Let's say I'm mostly interested in looking at power supplies, which usually switch in the 100s of kHz - 1s of Mhz range.
I just presented a module two days ago on EMC precompliance at our Demystifying EMC conference
I think it will be available on-demand at some point, and I'm planing on turning it into a YouTube video / whitepaper shortly thereafter as well.
In the meantime, my short answer would be that 1.5 GHz is probably fine for SMPS precompliance, for both conducted and radiated emissions.
Perhaps more important than upper frequency limit are the noise of analyzer and a good set of near field probes (and potentially a preamplifier, if analyzer noise is high or probe quality is low). A noisy instrument and/or low quality probes (or poor probing technique) are common issues in precompliance testing.