Well, Graham, while I agree that it might not be the best idea to touch the parts just to play with htem a little, your idea of spraying the whole sprue with clear doesn't sound good to me at all. Luckily for me most of the models I have built or plan to build in the future didn't/don't have the chrome sprue. But the ones that did usually annoyed me because under that lovely chrome finish you had flash, mold parting lines and other nice things like that. So the parts had to be cleaned up, filled, sanded and assembled and just then I could start thinking of rechroming them - I hope you see that at this point your advice isn't very helpful.
Here, let me post some pictures to cheer this thread up a little.
Those fuel tanks out of the box had a really ugly seam splitting them vertically - it was easier to scratchbuild them out of some plastic piping than filling and sanding the seams. After that they had to be rechromed - with Alclad 2 chrome. Some gloss clear went on them too - but it wasn't Testors - it was Alclad clear. Any clear always dulls down the shine a little - my trick here is to put a very light coat of Alclad chrome on top of the clear, that restores most of the shine. I know, it sounds funny, but works for me.
Here's another one:
Those bumpers had to be modified a little, and also did have a nasty seam line in the "wings" - very visible, so I had to sand them down and rechrome the bumpers. Again, I have used the trick with "alclad on gloss" described above
And the same model, rear view mirors:
The kit part (on the right) had a nasty sink hole right in the middle, thonseam lines along the rod and was molded with the door hinge that wa supposed to be body colour. To save time on fixing the issues I have scratchbuilt two new mirrors using some silver-coated copper wire for the rods and plastic discs for the mirrors. Those were Alcladed and ended up lookig good IMO.
And I also had a feeling, when I was removing the chrome from some parts, that many manufacturers already clear-coat them. So in the end I really wouldn't sweat it, and like I said I don't think clear-coating the whole sprue is a good idea. But of course you have paid for the parts so if you really want to...
Thanks for reading and have a nice day
Paweł