Need to recognise there's no difference to an instrument approach whether you're VMC or not. The only difference is that if you can meet the visual approach critera, you don't need to conduct, or can discontinue the instrument approach. Obviously that critera is different by night; hence why you're wanting to conduct an instrument approach rather than circle from LSALT.
The speed limitations are there to keep you within the area surveyed when they build the approach, just because it's VMC, doesn't mean you can disregard the speed limits, because you obviously still can't see terrain. In terms of a straight-in approach, they're there to set you up for a stablised approach and reduce your workload close to the ground.
I never saw it as a grey area, nor ever heard about it from any other pilots. I'd love to hear if anyone's view differs from this; I'd be quite surprised.