The golden domes above the holy shrines of the Prophet and his Ahl-ul-Bait and other respected personalities in Islam are a sign of their value for the believer who visits them. These personalities gave everything they had for the cause of Islam and without their selfless effort and sacrifice we would not be able to call ourselves Muslim today.
The gold, silver, gemstones and other artwork which can be found in the shrines and outside shows the deep love, respect and appreciation people feel for these special personalities.
To express love and respect, we always use valuable items to do so. Therefore, the husband presents his beloved wife with jewellery if he can afford it.
One would think that the money being spent to build and maintain the shrines could be spent better elsewhere. But this is not the case. In fact the shrines are not being built by spending taxes which would then be not available for projects for the needy. Rather they are built by the money people give to the shrine. Each visitor leaves behind a relatively small amount of money, which adds up to a vast amount as millions of people visit the shrines each year.
For example, here is a link about the shrine of Ali ibn Abi Talib, where the money being given in charity to the shrine is counted every Friday by volunteers. This link is in Arabic.
Many charitable projects are being financed by the donations. Here are some examples of projects, the shrine of Hussain ibn Ali in Kerbala, Iraq has paid for:
- Drinking water project (Whole of Kerbala has now clean drinking
- agricultural project
- Hospital, with state-of-the-art equipment, offering free treatment
- Kerbala airport
- Housing for refugees
- Military group to fight Daesh
and many more.
So the shrines are actually generating money rather than costing money.
The argument that gold is haram for men is not applicable here, as it only applies to wearing gold like rings etc.