Considering that the Spaniards got a quick interest in the Americas due to the discovery of precious metals in the regions of the Mexican and Incan empires, I believe that the discovery of a region where the amerindian polities were somewhat less developed might make colonization of the Americas much slower.
While the interest on precious metals was a real boost, it's still obvious by contemporary texts that a main interest of Spanish settlers was neither gold or silver as such but lands. Spanish (but also Portuguese) colonisation was made along the lines of the plantation economy development, as it existed in southern Spain, then atlantic islands, and eventually Caribbeans : it was mostly about sugar and other cash-crops plantations as wine, wheat, etc.
Again, not that the search for gold didn't represented a first phase of Caribbean exploration, but as it quickly fizzled, you had the establishment of latifundar explotation at such rate that it wiped out natives.
The search for lands didn't just, that said, found its origin in trade production, but as well as an ideological/social happenance : most of conquistadores were poor, or at the very least socially ambitious : in the late Middle-Ages/early Modern period, the marker of nobility and political power was the holding of lands and titles. While societally it evolved from this in Europe, the importance it represented for petty nobility and their hopes of social advancement was a real self-acknowledged interest : Cortés himself can mention gold mining and processing in Mexico in one page, while the description of lands, land-working and farms takes several of these.
Now,back to the point.
What did we have in East Coast at this point? While you had some chiefdoms around, it was still essentially an achrematic and relativelty acephalic ensemble of peoples practicing slash-and-burn agriculture for what matter northern-eastern coast, without important possibility of quick plantation economy : you'd argue that Caribbean territories weren't this much structurate, which is true, but it was eventually bolstered by the close presence of continental holdings.
The southern-eastern coast is more interesting : the Mississipi basin still held
develloped structures, even after the decline of the XIVth century in its southern part. IOTL, de Soto witnessed the ensembles builts around Mabila or Cooso.
It's not exactly something imperial and swimming in gold or plantations, but if Iberians settlers first met with southern-eastern Coast, you could see some reedition of what happened in Caribbeans : the contact with Mexican peoples is, IMO, unavoidable would it be only for the rumors of gold, further than these lands (and this time, true rumours).