The corrosive crud still gets onto your engine and into your electrics, the fairing just stops you from seeing it.
The Missus and me use the bloke from the All Year Biker website, he travels round the country washing bikes and spraying them with ACF50 from a proper compressor. I was dubious at first when we tried it but now we rarely bother washing our bikes, he comes and treats our bikes twice a year and each time they come up like new again.
Works out cheaper than getting through a can of WD40 every month as well, plus time saved where we don't have to spend ages scrubbing oily filth out of all the nooks and crannies.
I'd avoid Muc-Off as well. I tried some recently as my Fazer had got absolutely filthy over winter. It took all the ACF50 off so the all the bolt heads rusted and alloy bits started going white and furry over the next week. Definitely a product to avoid! Mild car shampoo is all you need. Never ever use washing up liquid either, it has salt in it to act as a water softener which will speed up any corrosion.
Another thing never to do is use silicon polish on painted parts, if you ever need to have a small paint repair done, the new paint won't stick, so you'll be looking at a full stripback and respray or a new panel, both very expensive.
Hope all that helps 
