What do I do with ascended mats from Spvp?
You can use the wiki to figure out exact uses, generally they are for ascended crafting or to go towards a legendary.
Yes most will require a crafting skill of 450 for dust/empyrial/dragonite to refine it to the first tier and 500 to use it for anything. Though the first two have ways of getting gifts out by feeding Mawdrey (takes a while to craft, may require living world 2) and the Wintersday quest reward (unavailable if you’ve not done it).
Clovers are quite rare, if you ever see yourself making a legendary hold on to them, even if it takes years to make one they can be handy to hold on to.
If you don’t care about any of this and are just staying in sPvP then feel free to destroy it all.