I dunno that I'd go that far. The later STs and early BTs, with the tail light wiring routed through the top of the frame, are otherwise just garden-variety K0s with low VINs. The STs are worth restoring however, it's mainly the super-early ones...with all of their unobtainium present & intact...that I'm talking about. The ones sans a cross brace might be rarer than perfect K3-76 headlight ears and those frames are decidedly at-risk. By all indications it appears that less than 500 were made...probably a LOT less. And the unique details are well-documented for these bikes. Ultra-rare and fragile is more consistent with a true museum piece, the kind of machine (and I can scarcely believe that I'm saying this) that should be preserved as a showpiece.
Restoring the later STs is challenging enough, when the rare bits are AWOL. But, at least the frames aren't fatally flexible above the top engine mount, the speedo dials, which are supported in two spots, don't break with use and you're not married to the goofy early-style muffler, or the early fenders. There's also a lot of uncertainty as to which running changes were implemented & when...so the restorer/owner has some leeway. These later STs typically command a modest premium. OTOH, they're not going to be worth less than the BTs, so it's not like there's a risk that you're investing in a lemon, either.
Now then, all of that having been said, bare frames...what the OP asked about...aren't likely to vary all that much in price. With the possible exception of an unbraced frame, or just the right buyer who wants a specific VIN range in tip-top shape, I'd reckon that clean, straight, & titled matters more...in dollars. In very broad, generalized, terms I'd peg a clean title at $200-250, depending upon locale, and likely to increase in the future.
As for bare ST frames, I don't see any motivation to start melting `em down. They're just not the precious ore that some had hoped they'd be.