Just the fact THAT the Armada has landed would be significant enough. Once word gets out that you CAN actually land a fleet in Britain, there will be enough other nations who will want to try for their own, even before Hitler... hell, even before Napoleon.
Just imagine: For every time England sends an army into mainland Europe to fight, another European nation sends an army to England. Even if the ratio of English armies going to the continent and foreign armies going to England is more like 2:1, 3:1, even 5:1, suddenly England isn't that separated from the rest of Europe anymore. So the wars of the Spanish succession would become a lot more interesting.
...
You don't actually know much about the history of European warfare, do you?
Trust me, the Continental powers did not spend their many wars with the UK declaring "And of course, invading Britain is RIGHT OUT."
It is just that reality got in the way, just as it did for the Armada.
Actually, as it did for all THREE Armadas.