Is it possible to "gamble" with Silverwastes?
Yes you can salvage Both the jewel and the seared ring and get the salvaged collection item from them.
Drop rate Research on this subject is rather difficult and I can’t give you any data on it. You would be salvaging between 100-120 jewels before you break even on gold (depending on the current price of salvaged excellence)
You might want to test-buy 10 green bags (bottom of second tab) and see what’s in them. Generally I get at least one T6 mat per 10 bags, as well as a number of other items of some small value. Compare that to the minimal crest/copper cost per bag. I don’t know what Jurah’s Jewel goes for, so I can’t guesstimate comparative profit percentages, but it does seem to me you get a more guaranteed return per expenditure with those bags than you would gambling for an expensive RNG drop.