Readerly dilemma

My voracious reading habits tend to pull me in two different directions: I reread a lot, so it makes sense to buy books and hold on to them, but I also have limited space, so I try to winnow books I'm not wild about so there's room for new obsessions. My dilemma is this: a series I used to like and reread often has gone completely downhill, and I stopped buying the new ones eight years ago. It's been five years since I last reread the books I do have. Should I get rid of the ones I have (holding on to the couple I like best), or should I hold on to them in case I get sentimental, so I don't have to re-buy the series?