Is there any benefit to adding anything to the intercooler spray bottle or shall I just keep it as water only?

 

I think Methanol has great evaporation, therefore cooling, properties. So you can put any % of it to the water... or indeed have 100% in there lol. But perhaps not, as it's nasty poisonous stuff and seeps through your skin, so be careful. Also high concentrations may gradually attack and 'melt' the plastic reservoir bottle a bit over time?

All that said, then just plain water is excellent for removing heat (as we all know)...

 

methanol also burns, so don't add that in in any higher concentrations