I have been to Germany and Spain both, a number of times.

I worked in Spain for a while too.

As the others have said, they are really really different in terms of culture, scenery, temperature.

In the 2nd week of July you will get great weather in both, but that is just before the majority of European school summer holidays, so you may find some resort areas of Spain choccas with UK tourists.

That said, if you want a "beachy /end of trip /relax on the beach/resort-like" type few days, you cannot go past Spain. I would reommend the TerragonaSalou/Cambrils area which is very close to great sights and close to Barcelona, and good clean plentiful family accomodation & fantastic beaches and restaurants.

If you want more serious "sight seeing"/art/culture, then head back to Germany.

If it were me, I'd be heading to Spain everytime!

(I am envious BTW!!)