Yeah, I would agree with this wholeheartedly. I have done a number of these trips France Spain Portugal touring as my parents live in Portugal. I would also advise you plan enough time that you arent pushing yourself each day (unless you like that sort of riding). Personally, I like plodding along at 50-60mph on A or even better on B roads. I like to be able to stop when I want without giving stuff about a schedule. That allows me to meet people which is all part of the adventure.
On my first trip I made a mistake of planning each day and ending up having to ride for 6-7 hrs at 70-80mph; something easily within the capabilities of an1150GSA (I have one too!), but the danger there is that you end up passing the real adventure by.
I am planning to do a trip to Portugal via France next year where we avoid all motorways and A-roads except where absolutely necessary. It will take us a long time but on the GS it will be fab.
From living in Portugal I would also recommend central Portugal. Get off the beaten track a bit as the food in local Portuguese restaurants is fabulous. Aim for restaurants where there are plenty of cars outside at lunch time as the Portuguese love good food, and will gather in the good eateries. Their cafe's are generally very good as they are fussy about what coffee they drink.
Finally, if you are going in the summer, make sure you have the right gear to stay cool as central Spain and Portugal are extremely hot. We were so hot between Caceres and Seville that at every stop we dunked our t-shirts in cold water and put them on again under our jackets!!
However bear in mind evenings and the possibility of cold or wet weather.
Am sure you will have fab time, and if you want any additional recommendations on Portugal or Spain that I can help with, feel free to drop me a PM.
Cheers mate
try to remember that your trip is about the "riding and roads" rather than trying to get somewhere. ~Enjoy the moment.
You might want to adjust your main beam so it points the correct way so as to avoid being flashed regularly at night.
Oh and fill up before you get on the ferry.