Contemplating visiting the UK, Spain and/or Portugal in September.
Interested in whether this is a sensible plan or whether I am delusional.
Nope I'd say it's all possible (even right now).
The UK has hinted that they've properly ended restrictions (and even their omicron restrictions were very mild/didn't last long), you don't require a test to enter and soon you won't require a test upon arrival.
Spain is similar, just an extra online form and you're good to enter, no tests or other cough required.
Portugal on the other hand has been slightly more annoying, the rules keep changing and different rules apply depending on how you enter (flying vs driving across the border) but I'd assume by September things will be better as the EU seems to be moving forward at a very quick pace.
The main risk I see is that of being infected just prior to travelling or during the trip.
Having just come back from Europe my logic was it's possible to get infected in Australia so it's not that much different. Obviously you'd be silly not to buy travel insurance (AFF has a great article on options that cover covid because not all do).
Technically you could fly to the UK/Spain without even getting tested so might not even know if you have it prior to traveling, medical care in all those countries is of a excellent standard and if you happen to test positive but aren't super sick the worst is extending your trip by 7 days (good travel insurance will actually pay for these extra 7 days + flight changes).
When I went over to Europe less than a month ago, I waited until actually arriving to organise the accommodation that couldn't be easily cancelled and airlines are becoming more and more flexible. Countries are constantly changing the isolation requirements and hopefully be September things will be even better, in Singapore now it's just 72 hours provided you don't have symptoms.
I doubt borders will slam shut as we have seen previously.
Both Europe and Australia seem rather committed to open borders, hopefully by then transits in Asia (such as a Singapore stop over) will be easier and require less paperwork/testing.
Entry into Australia is now the easiest it's been in the last ~22 months, one online form (which is replacing the arrival card anyway), proof of vaccination and a RAT test done less than 24 hours prior to departure for ~$30-40.