Friends, at a guess, would be Brazilians from the hinterlands (Fortaleza perhaps) where certain goods might not be so available, with a bit of money, but not enough (or not the inclination) to go abroad to Miami, where certainly prices for goods are much lower and many Brazilians shop in preference to any domestic city.

For a city of its size, Sao Paulo has museums that are sadly lacking in quality. Anyone who has had the opportunity to visit a city of that size (or some even smaller) in the US or Europe has had the opportunity to see great museums and their major works of art. MASP, Pinacoteca, smaller museums such as the Lasar Segall (artist's house), are however a good way to learn something about Brazilian art history and Brazilian artists such as Portinari, a seldom covered area in even university level art history courses.

It really depends. If you come to Brazil to hear the same old music you can hear in London or NYC, then perhaps clubs in Sao Paulo might be preferable. But if you travel all the way to Brazil and want to hear the unique rhythms of the country you are in, Rio is not lacking in any way on any night. There are plenty of venues to go dancing and listen to music styles from samba gafiera to forro to bossa nova to Brazilian funk and lots more--every night of the week. However, if you take advice from a guidebook aimed at party-hearty foreign tourists, you may never discover many of them.
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And since the OP describes himself as a "music maker", one more reason to suggest the unique musical culture of Rio.