The German green formed from an anti-nuclear movement and had a strong opinion about it that is not necessarily shared by the French Greens. Furthermore, the German Greens were in opposition when Germany hastily got rid of nuclear and are not responsible for how it went. When they last had to plan nuclear phaseout in the Schröder years, the result was a very long plan centered on building no new ones and letting most exiting ones do most of the planned runtime.The green don't make plan, look at Germany. They would have rush to shut them all down. There's also no reason to replace them, nuclear complement renewable perfectly.
It was a conservative gouvernment that made hasty and economically unsound decisions to appeal to the voter panic after Fukushima.
The purpose of the wealth tax is to tax wealth.The problem is that the wealth of rich is untapped, or rather, hypothetical money. Look at it this way, someone make a company, make it public and create share of it, the share price explode and now the company is worth trillions, government comes in and tax the unrealized gain for (lets say) 100 millions. That's no different than the central bank printing 100 millions, its creating money that doesn't exist and injecting it into the economy. And eventually the market would price in the wealth tax which would depreciate the value of share by quite a lot, people would move to other system to hold their wealth, system that would be harder for average people to take advantages of (it would also destroy the retirement of millions). The only good use of wealth tax is to force inactive asset back onto the market (ie land based) but land based tax are really complicated to implement and their own bag.
The higher the inequality, the more it hurts if wealth is not taxable because it means less and less assets and money circulation are accessible to be tax and thus to pay for the gouvernment expenses. There is a limit on how much you reasonably tax work before that is crippling the economy. And a wealth tax would not burden the middle class or their retirement plans at all. Similarly to inheritance tax there would be thresholds under which no tax occurs.
Sure, wealth tax has problems. One of them is the potential to drive wealthy residents out. Another one is that, indeed, it is inefficient because it would require to know how wealthy people actually are and estimate countless items that are not actually on the market. That is a huge bureaucratic undertaking and leaves lots of room for shady practices or unfairness (like, again, inheritance tax).
It is still worth it just to combat inequality. How else are we ever supposed to get rid of inequality or at least lower it ? It won't get better by itself, only worse because capitalism leads to wealth concentration.