They find the ore there, they're probably going to do some more exploring, find the whole Erzegebirge....
At that point, they're committed to holding Bohemia and parts of OTL Germany. Which is going to be a pain if they don't pacifiy Germany, so you might get a Oder border for the Empire.
All that extra silver might pay for the military expenses, and encouraged colonization of Germania.
All that extra land and the difficulty of travel overland will have people working on a Rhine-Danube canal and a Rhine-Rhône one.
Said canals probably don't have pound locks, at least initially, as they probably haven't been invented yet. So you'd need to portage at every lock. Which is still better than carrying everything by wagon the whole way. This would provide a LOT of encouragement for someone to invent a pound lock, which would massively improve internal transportation all through the land portions of the Empire.
This would be HUGE!!! IMO