Been an Iberia Plus client for about 10 years now. I traveled with Iberia at least twice every year and have only been formally upgraded once. This after spending, on average > USD 70,000 per year and accumulating an insane amount of Avios. Their customer service utterly sucks. Most of their first-line representatives are in Latin America and there's only so much they can do. If you need anything north of complicated, they will quickly transfer you to someone in Spain where, depending on the employee and their inability to speak English, they will hang up on you every third call. Especially if things get complicated.
To top it all off, and after missing connecting flights 5 times in a row, we decided to file claims, which we were paid for. BUT! Little did we know that Iberia was paying attention. All of a sudden, out of the blue, Iberia stopped sending my wife (who has a separate Iberia Chase card) and I our annual USD 1,000 gift card (they sneakily advertise it as a voucher, but it is a gift card with very limited usage.) As of today, they owe us 3 gift cards and after 5 accumulative hours on the phone with Chase and Iberia, we're not even close to getting these gift cards.
We got so fed up with Iberia that we went to Chase, our bank, to file a complaint. Then, out of the blue, Iberia decides to make up a gift card # and sends it to Chase. BUT! The number does not exist.
If you DO decide to get an Iberia Plus card, understand that this is horse-manure you will have to deal with. Nothing and no one will prepare you to the depths and the limits Iberia employees will take you to in an effort to just get you to desist on any issues you may want to resolve.
You will be 100% better off with any other program.
Good luck.