This is a very interesting WI with a wide cone of plausibility, I think. The effects of the Peninsular War on the Spanish Empire can't be underestimated with the mass formation of juntas and collapse of "legitimate" authority and all, and before that point most discontent against the Spanish Empire consisted either of conspiracies planning revolution or of local rebellions against Bourbon centralism. I suppose the main exception to this is Argentina, where after the 1806 British invasion there was a massive surge of local pride that concluded with the Viceroy of the Rio de la Plata being deposed and replaced with a local popular military leader, with the Spanish authorities accepting this. That's the sort of precedent that might conclude with independence if the Spanish eventually try to truncate this sort of pseudo-autonomy and mess it up hard. Another thing to keep in mind is that, during the Napoleonic Wars even before the Peninsular War, there was a massive spike in smuggling to British and American markets. So if the Spanish try to deal with that and mess it up, that's something that might create dissent. But other than that, it would be a long process - decades, I think - to get the critical mass for independence, and liberalism and nationalism would both be far weaker forces in the Spanish Americas. I suppose Britain would also be eager to egg on the independence movements to commercially dominate the newly independent states - a policy which Lord Selkirk wanted - and that will have some effects.
Now, would Spain see the tides coming and commit itself to reform? Well, I don't know, this is something that would totally and utterly change the character of the Spanish government. Charles IV is likely king to his death, with Spain just trotting along, and Ferdinand VII would be king for a comparatively shorter period. I think the ideological foundations of the First Carlist War don't exist here with a significantly different (and probably more conservative w/ no Cadiz Cortes) Spain - but would Ferdinand VII have a son instead of Isabella II, would he have no children and so the crown goes to the Don Carlos of Carlist fame? Well, this is all post-POD, it's whatever you want I think. I have a strange image in my head of Don Carlos getting the throne and repealing the Bourbon reforms, and along with it giving the Viceroyalties fueros giving them similar feudal autonomy which allow for them to get independence like British dominions. But that's just one possibility (and I don't know if Carlos would be as into fueros without the same circumstances). But that's just one possibility, and it would be very much in character for the Spanish monarchy to alienate the Americas. But again, it might be decades before that comes to pass.
As for the American Northwest, well I suspect Spain won't colonize it much. Perhaps the missions in California get expanded northwards - hell, perhaps with no or an alternate Adams-Onis Treaty due to Spain having a stronger position, it builds some in Oregon - and, with Northern Mexico less disrupted by Comanche raids, there's some ranching expansion northwards (along with the fur trapping in New Mexico) but beyond that, Spain has very little reason to focus there when it has such a large empire elsewhere. I think when the gold gets discovered in California (perhaps with Spain discouraging settlement in favor of its missions, gold gets discovered first in Oregon and tapped in CA later?), there's going to be an uncontrollable wave of settlement. Sure, more of that is going to be in the Pacific part of the Spanish Empire here - more than the important Chilean migration - but a lot of Americans would still come in with large numbers, and that would destabilize it. And while Spain is likely to be a lot more restrictive to American settlement in Texas, it's still going to be coveted and face filibusters and the like, and if there's a Californian crisis American designs on Texas are going to come up.
I don't really think Louisiana is important to this anyways, as it was never treated by the Spanish as much more than a shield for its much more important colonies in the Caribbean.