Once humans can reach one asteroid in its native orbit, the gateway is opened such that hundreds (if not thousands) more will be accessible, enabling a steady programme of exploration to be unrolled in the late 2020s and 2030s.
True, but only one of those - ACE - provides definitive storm strength and arrival time, by sampling the solar wind directly upstream of Earth for magnetic field & plasma properties (density, speed, and temperature). SOHO and STEREO let you know that something left the sun using imagery and estimate the arrival time. All of those are old NASA satellites long past their design lives, and never intended as reliable weather forcasting assets. The Deep Space Climate Observatory (DSCOVR) will take over for ACE next year.
Grid operators respond by reducing the output of baseload power plants (nuclear, coal, etc.) and bringing up small local generators (e.g. natural gas) to reduce the load on long distance transmission lines and their transformers. That is sufficient for the more common small events. Probably not for events like Carrington and the May 1921 geomagnetic storm, but at least they will be in a position to respond. The big danger would to be blindsided because the government couldn't get their act together enough to fund reliable forecast & warning systems. The worst events can take as little as 18 minutes from a satellite at L1 to Earth.