From your post: "I’ve had Catalan people tell me they prefer to speak English with me rather than Spanish"...."My experience is you will have to work very hard to befriend a local"
I think that this summarizes clearly one of the biggest issues: Real integration.
On the other hand, everybody in Madrid is from another part of Spain, and nobody has a problem with spanish language therefore is much easier to integrate and to make friends from different places. As said, the city is a furnace in summer, but is not much different to most places in Spain (including Barcelona). Maybe Madrid is a little hotter, but Valencia's beaches are at 1:35 h of distance in train, and Barcelona and Malaga at 2:45 hours or so from Madrid.
If you want a super-nice summer climate go to the Cantabrian coast, when it rains all day long each four days and you can sleep all night long :-). Irish climate.
Personally, I receive a Startup Digest newsletter tailored for Madrid and BCN, curated by Alex Barrera, who I think is famous in the startup scene, and Maria Encinar. They cover jobs, rounds, events and talks...the usual. That might be interesting for you.
moved to Barcelona about two years ago (from London). Here's a post I wrote last summer about some of my impressions. http://www.freyfogle.com/post/1466857133/moving-to-barcelona
In short: quality of life is great, and the tech scene, though still small, is growing rapidly.
For the Barcelona I highly recommend you subscribe to this weekly newsletter http://www.barcinno.com