Thats a good route - Madrid is a good hub to travel on to Central and South America. It makes getting to places like Mexico, Peru, Cuba, Chile, Argentina, much easier. Its also a beautiful and good value city itself!
You might think you know about economics but you sure as hell know nothing about long haul air travel.
So you want to organise your trip to say Buenos Aires EZE using this flight from Cardiff.
Flights all have to be booked separately as there no through ticketing, a bit risky but lets do it!
You must fly on either a Thursday or Sunday which is a bit limiting. Then you arrive at Madrid, your Bags not through checked, out of the terminal and customs then back in at midnight and then you discover there are no direct flights from MAD to EZE any how and you have missed the last 1 stop flight via Chile.
Me, I would drive to Heathrow terminal 5 and get a non stop BA flight and be there cheaper and a lot quicker while you are bedded down in Madrid terminal for the night
The route is a tourist route to Madrid, end of.