One never knows what to expect from a "derbi", and you just mentioned two. About the Catalonian derbi, although this match is really important for Espanyol I don't think Barça will relax their game because mathematical victory gives a lot of peace of mind; but who knows, Espanyol could try to do their best and eventually get a point from a draw.
Derbi is important for two engaged clubs and they usually fight very hard to win any debri. Barcelona don't must to win this derbi to win La Liga, they can win La Liga with another match. However, with importance of derbi, they will surely want to win it. Moreover, they will want to help Lewandowski to beat Benzema in Pinicchi race. In this week, perhaps Benzema will be reserved for Champions League semi final and Lewandowski will have one match to secure his first position in Pinicchi ranking.