Spain having many, albeit somewhat poor provinces that nevertheless have plentiful manpower, propped up with gold income will have exacly the effect I want it to have:
Spain will do tremendously well in the early game, where tech differences are minimal and inflation hasn't hit yet, and with the flood of Aztec gold and the rich Low Countries to offset that inflation somewhat, will rapidly become a superpower. Spain then embarks on conquering North Africa. Then they will lose the low countries, inflation will catch up with them, and we won't even need fakery like the State Bankrupcy event. They'll be stuck with a lot of poor provinces, many with the wrong religion and culture, high inflation and a dependency on gold income.
The reason why Spain does ahistorically well, and ahistorically poorly in the early game, is because this cannot be accurately portrayed with the current number of provinces in Spain. Right now Spain has a handful of rather rich provinces, which regardless of what happens will always keep them powerhousing along tech wise, and has to be artificially handicapped with stupid events in order to force them into decline, instead of their decline being the inevitable result of their circumstances and decisions.
Portugal is the same, Portugal was actually quite a poor country, but because their country is "compressed" into three provinces, they are artificially rich. Portugese provinces should be about half as wealthy as they are now, and Portugal should not be a 'small techie-beast' like it is. Also Portugal is a reasonably large country. Best solution is to add two provinces.
Gameplay concerns are my primary concern here.