Sure, w/o a doubt, the barrel fit & lockup, bushing fit to the slide & to the barrel & barrel quality are probably most important, but if the slide to frame fit doesn't matter, why is it done by virtually every competent GS that builds a BE gun or other "high quality" custom gun? Or higher end production guns, like DW, for example?
MM
As you said, other items are more important, but the "why" fit the slide to frame is an interesting question. Maybe the best answer is considering the diminishing returns on money spent, if slide to frame fit contributes 10% that's a big chunk and I want my gunsmith to go after it.
Also a well-fit pistol will last longer, and there's the matter of gunsmith professionalism - it the fit anywhere can be improved just do it. Melted Bo-Mars don't add to function of a pistol, but fit them properly anyway.
You mention BE gun's, if the Ransom Rest is still the standard of accuracy of BE then slide to frame fit plays a huge roll. Ransom Rest groups can sell pistols. Also, there are plenty of gun owners that can't judge barrel fit, but become an expert if the pistol rattles.
