If you're looking for spectacular views, I'd probably recommend another sleeper train, to be honest.
Booking a good bit in advance is usually one good strategy for a lot of European trains if you want to save money. But there are plenty of other options. Slower trains, off peak times, budget brands like Ouigo etc. can make train travel very cheap. If you want the flexibility afforded by a Eurail pass, there are country-specific options that not only give more flexibility than Eurail, but are also cheaper and don't require a supplemental charge for most trains. Discount cards are another big one: you can easily get 20-50% off the "normal" price with some sort of discount card, like the Carte Jeune in France.
Good luck with whatever your train travels might be, and feel free to ask me whatever!
[0] https://www.seat61.com/trains-and-routes/sud-express-from-ir...
I'm not sure why the article says you can take a normal train from Coimbra to Hendaye, there is only a night train, though it does have seats (not recommended, take at least a couchette or bed). Currently suspended due to corona afaik.
>"The specific country level passes, as well as buying discounted tickets, will nearly always be cheaper."
Whats the discount are you referring to here? Is this just the booking far in advance discounted rate or something else?