Some modern cars have fuel coolers fitted, not investigated where they are placed in the fuel system, but it means a real issues does exist.
Modern cars have a huge advantage in EFI,so the fuel never sits in one place, most fuel doing a circuit and returning to the tank. add to that it is sitting around 3bar pressure which will raise the boiling point by about 30 degrees should there be any localised hotspots (but I don't think the higher BP is requied, otherwise the fuel would vaporise after the PRV)
I have wondered if it is possible to set the carbs up to have a return fuel line. Probably more complicated than it sounds as you don't want to pressurise the float chamber at all, and you can't really use gravity for the return line. Not sure a suction pump would work either...
No this is far too much effort. I'd personally concentrate on reducing heat. The 1500 engine will always have the problem of having the inlet manifold right over the exhaust. If you can reduce the effect of heat soak on these areas it will help. You could zircotec the manifolds but this isn't cheap so I'd stick with better heat shielding and even go so far as to try and find fuel with a lower ethanol content, though this can be tricky.