I hope this is just a temporary - that you will give us both manual exploration and "trade node region" automatic exploration in the future?
I would actually like to propose keeping this system but making it available to everyone.
By having hard limits in place as to *where* you can explore, it makes less and less sense to have another hard limit that requires you to have a specific idea.
Allow anyone to hire Conquistadors and Explorers. They already get less pips now, anyway.
Allow anyone to explore, within the limits now based on your Colonization Range. Maaaaaaaybe allow Exploration to go just a bit further than Colonization, 10-20% or so.
Though you might want to put a limit on Conquistadors too... A natural limit would be to not have those forces reinforce troops. I mean, how am I capable of sending reinforcements to my small force that's miles deep in the South-American outback anyway?
Change the Exploration idea and call it Colonization instead.
Change Quest for the New World so that you're allowed to have a Conqiustador or Explorer for free, ie. not counting for your Leader cap. Other bonuses are of course possible, but this one feels best.