Playing with Venice in 1.5, re-elections + joining the empire got me into the New World in Greenland by late 1479 despite going over #relations limit. A quick look at the map at that point showed that this actually was before Portugal managed to drop a colony in Brazil, meaning Venice literally colonized the new world 1st

.
It would be hard to argue that going exploration isn't worth it if you can pull that off...once your colonies are overpowering they'll have to either come into the Mediterranean or beat your larger colonies for war score. Neither is plausible.
The money in Gulf of St. Lawrewnce if you have NA monopolized and direct --> collect there is pretty impressive.
And man, I'm starting to adore merchant republics. Money is nice, but MP control (with a high-floor if you understand the tradeoffs on reelection) + no regencies ever is great. I wish there weren't so few of them.