I live in Europe. I have travelled in Europe immensely over the last 15 years. I would NEVER recommend anybody this strategy, ESPECIALLY if they're coming from outside the EU.
The main thrust was about finding a big car park outside of the historic centre and use your legs. Not sure what is objectional about that
(I'm also European if we're doing that)
When visiting Europe, I mostly avoid cities, but when I visit them, I usually take public transport. (Yes, if you stalk my comments, you'll see I make an exception occasionally). I've parked at various train stations in Europe and got the train in, especially the bigger cities
Outside of cities (e.g. the coasts) I usually rent a car, and park in the cheaper spots and use my legs.
I'm generally pretty tight when it comes to paying for parking. 15 EUR a day is my limit when travelling so usually find cheaper alternatives even if it means more walking
At home in the UK I walk, cycle, take the train and drive. Again, I tend to avoid cities but yes I do use Park and Ride sometimes when I drive. Or I park on the outskirts during free periods (e.g. Sundays).
On top of that, I live close to amenities and walk everywhere for shopping etc. It's not flat either.
Satisfied? :)
Outside of towns and cities the road networks in those countries are generally excellent. Especially in France and Italy with their toll roads.
If you're just going city to city, take the train.
I've driven extensively in Spain and to a lesser extent France, Italy and Germany and never found parking a "joke" except in cities or with a huge car. Of course, due to density, the free parking places are usually very busy and hectic. But there's always an option to pay/pay more