Those negative prices are always on the spot market, the bulk of the energy you get from your supplier was paid for in advance because it's generally cheaper and if your supplier is buying lots on the spot market, well, spot market prices would not be that low.

In a sense it would make sense to lower the price for the consumer, have some smart devices use it up (e.g. an already-loaded washer, an already plugged in EV) but most places don't have that kind of tech installed (yet) and even then it'd be cents, and you don't want consumer prices to oscillate too much. Also, the total impact is going to be limited, who the hell gets off the coach to load their washing machine with half a load just because electricity prices are low. Or re-schedules making pizza.

What makes a lot of sense is having large-capacity storage systems which can soak up this kind of seasonal load. They don't need to be particularly efficient, it's more important that they have a large capacity, both in terms of Watts and Watt-hours. Things like flow batteries. Many district heating systems actually have a giant water kettle just for this reason: Absurdly cheap to build, usually it's just standing around doing nothing, but when electricity prices go negative they can sink tons of energy into water and use that to feed showers for weeks to come. Not the most efficient use there is but it's a start.