I don't remember a team that had a season as surprising as Borussia Dortmund. Maybe Stuttgart may be providing this in a positive sense because they are better than expected, but in a negative sense I think one of the biggest surprises belongs to them. Borussia Dortmund are now far away from their goal of winning the league title. For the top four, they will have to beat Leipzig. If they play worse in a few games, I'm almost sure we won't see them in the UCL next year.
That is the biggest worry for Dortmund fans this season, that their beloved club is losing the potential to appear in the UCL next season. Regardless of their luck this season in getting through the UCL group phase, in the Bundesliga they should also be able to achieve the same good balance. A situation that is rarely experienced by Dortmund, because usually they appear consistent and compete closely in the hunt for trophies with Bayern Munchen, we can take an example like last season. Stuttgart and Leipzig will continue to try to assert their position in the top four, because they also want to experience the atmosphere of the UCL next season.
Dortmund have to do something, I mean looking for a solution in the transfer window if they want to appear consistently, using the existing players alone, which in my opinion is not enough to compete in the second half of the season. I think they don't really understand that this season Bundesliga competition is very different from previous seasons, if they hope something good will come without trying for it, then they will sleep for a long time this season just dreaming.
That close competition you are talking about ended without success for 11 years in a row and Bayern Munich won the Bundesliga title every single year. It sometimes looked close, but Dortmund never won it. Now it is beginning to get serious for Dortmund and they have four games now that are rather easy and should be won. If they don't at least get 10 points out of those four games, I doubt that this is going to end with the qualification for the Champions League this year. They have all the hard games towards the end of the second half of the season and I doubt that they will win a lot of those games against teams like Stuttgart, Bayern or Leverkusen.