I have some foldable racing tyres, still with plenty of tread but with some small cuts through the tread & cloth. Can I do anything to them or are they destined for the bin?
You should be able to patch the tire with a tire boot, which you should be able to pick up at your LBS. It's basically a rubber patch that you apply to the inside of the tire, where a gash is. Similar to a tube patch, but thicker. There's all sorts of things that people use for makeshift boots, too, such as a $1 bill. The important thing with a boot is that it prevents the tube from herniating through the gash.
If the cuts are very small (1mm as you posted above) then there's not need to do anything. Normal punctures -- especially from glass -- are liable to leave that size of cut. I've used a tire this season for at least 3000km which accumulated many such minor cuts -- I only replaced it last week because it was getting far too thin.
You'll want to watch out for larger cuts though -- anything that the tube might bulge out through. The sidewalls are especially susceptible to this since they're thinner and gashes squeeze open wider where the tire meets the ground. My rule of thumb is if you can see the tube through the tire, even if you have to pinch it open, then it's probably done. Put a tire boot in to limp home but replace the tire as soon as possible.
If you can see cloth, I'd be seriously considering replacing the tyre.
While it might have lots of tread, a deep cut is going to be an area of weakness and while you might be able to back it with tape, notes or similar padding, the tyre will not cope well with high pressure - and will be much more susceptible to rupturing at that point.
And make the next set of tyres you buy Kevlar-lined, it really does make a serious difference to longevity.