I picked about 20 5 gal buckets of grapes and will see little white spiders, earwigs, dust, crushed dry grape leaves, little stems, etc in with the clusters. Is it recommended to hose these down gently before putting them through the crusher? Is it important to let them dry off before putting them through the crusher? The hose water is potable.
Absolutely DON'T wash your grapes.
In my vineyard/winery, we feel that if you have to wash your grapes then they aren't worth making wine with them. Detritus will always be part of the 'art' and 'unpredictability' of making wine. Plus, traditional wine makers, feel that all that 'stuff' contributes to the essence of the wine. Washing them will definitely water them down.
One can wash the grapes to remove "detritus from the field" but it is not really necessary unless the grapes are horribly soiled - and then one might ask why one is making wine from them anyway! But it is possible to wash grapes and if one does it is also a good idea to let them dry as far as is possible to reduce extraneous liquid diluting the must.
In normal situations the skin of the grapes contains natural yeast that is used to ferment the must. So washing the skins may also require extra yeast to be added to the must to get it fermenting vigorously from the start.
Grapes used in commercial presses have a reasonable amount of detritus with them and no effort is usually made to wash grapes for commercial brewing. They often go directly from tractor-trailer to wine press and the only "cleaning" is done by filtering at a much later stage. Traditionally grapes were pressed under foot in a tread press and one might imagine that process added quite a lot of extra bits to the must. But the wine still turned out well!