Looking at the Portuguese and Brazil. Yeah, it won't be all *that* exciting, with them not finding empires of gold and silver, just relatively simple natives, and also at the same time reaching the *real* Indian, China, Indies, and Japan.
But Brazil would not be worthless, and there would be no pesky Papal line of demarcation saying "STOP! at this part of the coast". Brazil would be a station for emergencies on the around Africa route where ships could take on fresh water. The Portuguese would totally set pigs roaming free to be a food source for future intentional voyages and castaways (I think they did this and the Spanish did it all over the Caribbean. They would notice the Brazil wood and its useful red dye and harvest it on stops. They might set goats free for another meat source.
They would probably interact with the natives enough over time to learn about maize, cassava and sweet potato from them, which they can all grow in other places. In any permanent stations on Brazil's coast they would plant cane plants for sugar, the main challenge would be keeping up a labor supply to cut and process it.
Then things become a question of how long after discovery and setting up a few settlements in Brazil do Portuguese captains decide, hey, let's find out the dimensions of this big island and try to circumnavigate it? They may not need to expect a great bg civilization in order to do that. Mostly geographic curiosity could motivate a look pretty far along the coast. If they get far enough to the north, they could find the Muisca in Colombia. Far enough south and around to the west, they could find the Inca. Then it all becomes *very* interesting. Timescales could vary quite a bit.