Some of you are thinking in terms of duniya only. Yes, more wives mean more expenses. This is why the kuffars are not having more kids, it means more mouths to feed and clothe. But we Muslims do not think that way. We know that rizk is from Allah alone and we all come to this duniya with our own share of rizk. When we re in the wombs of our mother, our rizk is declared and written down before we are even born. So more wives or kids will not take your rizk away from you, rather they have their own rizk they bring and Allah will increase your means of earning so they can get their rizk through you. This reminds me of a beautiful hadith I read a while back. A poor man came to the Prophet (pbuh) stating his condition and was commanded to get married. He did but his situation did not change so he came again with same complaint and was advised to marry again and so he did, but it still didn't change his condition and he came again and again he was advised to get married. After his third marriage, his condition began to change and things started to look up. Each wive brought their own rizk, the third one was probably more blessed and brought enough blessings that everyone was happy.
Regarding doing justice to the wives and treating them equally. It seems you had a negative impact on you brother Hard Rock Moslem. Just because you have seen injustice does not mean that is the norm. A man's heart may incline more to one of them than the other. Allaah says (interpretation of the meaning): “You will never be able to do perfect justice between wives even if it is your ardent desire” [al-Nisa’ 4:129]
An yet Allah still allowed polygyny stating if you can be just to them. Islam requires the man who has more than one wife to treat his wives equally and fairly. What is meant by that is fairness with regard to spending the night, accommodation, spending and clothing.
Al-Shaafa’i said: The Sunnah of the Messenger of Allaah and the view of most of the Muslim scholars indicate that the man must divide his time, night and day, among his wives, and must divide it equally, and that he is not allowed to be unfair in that.
Ibn al-Qayyim (may Allaah have mercy on him) said: He (peace and blessings of Allaah be upon him) used to treat them equally as regards staying the night, spending time with them and spending on them.
Ahmad said – concerning a man who had two wives – he has the right to give one more than the other with regard to spending, desire and clothing, if the other has enough, and he may buy a finer garment for her, so long as the other has enough. This is because it is too difficult to treat them equally with regard to all these matters, and if it were made obligatory he would not be able to do it, except with great difficulty. This is why it is not obligatory, such as treating them equally with regard to intercourse.
Al-Nawawi said: Our companions said: If he treats them equally (in the matters where that is required), he does not have to treat them equally with regard to intercourse, rather he should stay overnight with all of them but he does not have to have intercourse with each of them. He may have intercourse with some of them when it is their turn for him to stay with them and not others. But it is mustahabb for him not to neglect intimacy with some of them and to treat them all equally in this matter.
With that said, this isn't for everyone. But for those who do wish to go with it, islamic guidelines are provide on proper conduct and rights of everyone involved. Anyone who does not follow them is only putting himself in jeopardy and will be held accountable for on Judgment day. Otherwise, if someone wishes to engage in it then we should pray Allah make it easy for them as we do have a need for such in our society today, especially with the invasion and occupation of Muslim lands resulting in thousands of orphans, widows and refugees. Allah says there won't be "perfect justice" but so long as we do what is required and what is in our capability, then inshallah it well not be held against us.