What do you mean by, "Elite Treatment"? Being Elite doesn't give you treatment like a royal. What is more likely to happen is as IbPlus Platino you are likely to be treated better than a regular pax - but don't expect a personal treatment on each flight.
If the purser says hi! Thank you for flying Ib as a Platino member, it should be considered a success.
You won't be upgraded since there's no First Class on Iberia flights.
You will have preferential access to customer service at the airport and a special phone line.
And there's just one business lounge in Madrid - no Sapphire/Emerald separation.
Aer Lingus is good for Aer Lingus and likely for the other carriers on the TA joint venture once Aer Lingus is accepted. However, if you ever intend flying with other oneworld partners, there's "nada".
But it really depends what you expectations are by "Elite Treatment".