Spain's monarchy is very opaque. This has always been the case, but owing to the crucial role played by Juan Carlos during the transition to democracy and helping to prevent the coup in 1981, the monarchy was largely unscrutinised in the Spanish media and by many Spaniards for decades. This all changed when Juan Carlos (who was the president of the World Wide Fund for Nature) was photographed hunting an elephant during the eurozone crisis on a visit to Botswana that was effectively being funded by the Spanish taxpayer, at which point the Spanish monarchy became a more polarising factor.
Studies conducted by a number of Spanish political scientists have shown that the younger you are and the more left wing you are, the more likely you are to have a negative perception of the monarchy and prefer a return to a republic. This may not seem important, but for contemporary Spanish voter preferences, this is massive shift and has not previously been seen in post-Franco Spain. King Felipe has been under a lot of pressure to restore confidence in the monarchy, but became a controversial figure himself, especially in Cataluña, owing to his role in the indepence crisis there.
As a result of all of this, it would be expected that the Spanish monarchy might be more keen to modernise and become more transparent. However, this has not yet occurred and there are lots of questions about money, corruption, and finances in relation to various figures in the royal household, not least Juan Carlos himself, who conveniently abdicated and moved to the UAE.
The UK monarchy certainly does bring in a lot of tourist money. Whenever I hold the monarchy/republic debate with students, one of the arguments in favour of keeping the monarchy is the income from the tourist industry. It is a strong argument, but the question remains as to whether the monarchy will remain as popular with Charles as king. Much of the popularity stems from favourable public attitudes towards the Queen. Charles was previously a much more divisive figure.