Spanish wealth tax is not as bad as all that.
First, the allowance is 700K per person, plus another up to 300K for your primary residence, if you own that. So that's 2 million out of the way.
Second, the rate starts below 1% after deducting the allowance. If you have 3 million you would probably be paying more like 6K a year.
Third, the tax is regional. In Madrid it currently isn't levied at all. (But in Catalonia the allowance is only 500K!)
Fourth, it only applies to readily available wealth. If you put some of your money into life assurance schemes that can't be touched for 5 years, that can be excluded from the count. I'm guessing that someone with 3 million can probably put 500K in a long-term freeze like that.
Fifth, there is a rule that your income tax plus wealth tax can't exceed 60% of your taxable income. So if you live mostly by making occasional sales of capital assets which are invested in growth funds, and hence don't have much in the way of taxable income from interest or dividends, your wealth tax payment will also be limited as a result.