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Arguably, yes.
The basis of the argument is a relatively simple question: Is being wealthy in and of itself a virtue or beneficial in some way?
The seemingly obvious answer would be "yes," but is that really true? Imagine you were a billionaire who was friendless, suffering from multiple physical and mental maladies, and burdened with having to work 16-hour days lest your pile of wealth evaporate because you were not actively managing it. Would you call yourself "rich" in any sense except for the numbers in the (Cayman Islands) bank accounts? I wouldn't.
What a robust body of research finds is wealth subjectively improves people's lives so long as that wealth can be translated into SOMETHING ELSE which actually makes people's lives better. If you are hungry, wealth buys you food. If you're cold, wealth buys you shelter and clothing. If you are sick, wealth buys you medical care, and so forth.
But what researchers find is that once people reach a certain level of wealth (roughly corresponding to a secure middle-class lifestyle in a wealthy industrialized democracy), additional wealth provides very little additional personal benefit. Being a millionaire is awesome. Being a multi-millionaire is about as awesome as being a millionaire. Being a billionaire simply gives you that much more wealth to protect from grifters, theives, etc.
What people who have significantly more wealth than the minimum amount necessary for maximum wealth-purchased happiness typically end up doing is one or more of three things:
1) Getting into social status competitions where their wealth buys Conspicuous Consumption. Larry Ellison didn't sell his $50 mansion and build a $100 million mansion because he needed it. He did so because a $100 million mansion is $20 million more than Steve Jobs' $80 million, thereby proving that Ellison's d**k is bigger than Jobs'.
2) Purchasing power over other people, either through philanthropy or direct purchase of government. Once you own all the homes, cars, yatchs, etc. which establish the size of your d**k, the next step is to purchase control of society. Either by using money to dictate the political process, or by using money to dictate which particular "good causes" are well-funded.
3) Ensuring future generations of Special People (typically family) get the benefits of the wealth without having to go through the ugly nasty process of either providing social value or winning a competitive "tournament" to actually win it. Of course, people who do this will fervently claim that American society is meritocratic if ever questioned about the fairness of their nepotism.
So, yes, Michael Bloomberg is arguably "too wealthy." He has vastly more wealth than can benefit him in any tangible way, and the purposes to which he is likely to put the wealth that ceases to genuinely benefit him are arguably either wasteful and pointless, or a demonstrable net harm to others and society.
As long as a person got the wealth in a legal, ethical way....good for them.
