Comment The Pioneer and Voyager probes (Score 2) 6
Although it would be wonderful if we could retrieve them, realisically we can't. And if we could get something to them to fit new nuclear batteries and replacements for components that cannot be revived, we could get newer probes out there with better sensors and a more powerful nuclear battery that could last a lot longer.
Having said that, I honestly wouldn't trust any of today's manufacturers to be capable of building anything with a comparable level of robustness, so a recharge mission isn't quite as stupid as it sounds. Almost, but not quite.
Still, fresh probes sent into the Kuipier Belt and the Heliopause would be extremely interesting.