I am totally in agreement, that nuclear plants shouldn't be shut down before fossil ones.
A decentralized grid sound way more resilient, then one with a few nuclear plants, which often have long unexpected downtimes (see France). I agree with you on the potential logistical dependencies, however that sadly applies to nearly everything right now.
This year again multiple nuclear plants in France had to reduce their output due to heatwaves and water levels, and ongoing cooling concerns. This is becoming a yearly occurrence. Though, I am not saying you can't have a nuclear grid, or you shouldn't use it at all, it's just that renewables seem to be a much better solution for most cases.
Yes, interconnectedness is critical if you want reliability.
Spain has far too little transnational capacities. That was a significant contributing factor in the grid outage.
The French grid has been extremely resilient with only a minor setback a couple years ago when multiple plants were in maintenance at the same time and that’s despite not significantly investing in it for decades.
Technically, a grid based on nuclear production is also a distributed grid. You have multiple plants and it’s easy to add overcapacity to the grid because nuclear is easy to modulate.