IB has a good lounge in FRA T2. It is modern, was only opened 6-12 months ago, good drinks, snacks and newspapers, and is almost never crowded. Dont know whether Sapphire gets you in, but IB is never strict on anything, so I think you have a good chance.

There is an excellent F CX lounge and an average BA Loubnge, but both are in the non Schengen sectors, so you will not be able to get in unless you arrive in FRA from outside Schengen.

Terminal 2 in FRA is rather empty, has few shops or bars, and is a desert after you go through security control (Schengen section). Go only through if you want to go to the lounge.

BCN lounges are also modern, but a bit dark (no windows). If I remember correctly there are no lounges in PMI, which is starnge considering that IB is one of the biggest customers of the airport.