First of all, try and find out what the poster GarySFBCN thinks – he has bought a place in Barcelona this year and should have some interesting opinions for you.
Hard to say what the long term will bring, if you are concerned about fluctuations in property value. What may be more relevant is if you can sell a property within a time-scale if you need to get out. Worth monitoring the number of houses sold on this site – they’ve begun to recover over the last couple of months after several years of falling demand but who knows if that will continue into the future? (see for example https://www.spanishpropertyinsight.com/buff/2012/10/15/balearic-home-sales-soar-by-32pc-according-to-recent-report/ )
Two things that we know of that may impact on Barcelona and Catalunya. One, the high speed rail link to France opens up from April next year. Unless the French economy tanks (and that is a possibility) expect to see yet more tourists coming down to Catalunya.
The other thing is the call for independence. This could have a serious detrimental effect on the economy in the short term as a lot of Catalan sales are to other parts of Spain, and a boycott could well arise. Also the EU are playing hardball on separatist movements and things could get very shaky.