I was working on a tango showcase before my fallingout with my instructor.
Yes my other dances started to suffer as the date was drawing near. At least a couple of steps that I had only recently learned I forgot completly which means a few hours turned out as a complete waste of time.

But it did help me.
Yes many steps I couldn't dance with other ladies. But since before we fought my instructor had done a wodnerful job she had insisted on me learning to properly lead her into these steps and always tried to show me where it was possible which part of our syllabus these steps were based on/adapted from so I would also learn something useful for later.
But the showcase training was also a great confidence boost. Mostly because suddenly all the ladies decided I must be pretty decent at tango if I am working on a showcase and started trusting me. And it is far easier to lead a lady that believes you can lead her than one who believes that no student can ever lead her as well as her instructor etc. And since one dance goes well the rest will follow. I noticed that in that group, once it was accepted that I was quite good at tango everyone deduced that I'd also be good at waltz and foxtrot which in turn I became better at more rapidly...