In a short answer, I would say no.
Generally I would never try to discourage anyone from wanting to see something for themselves when traveling. In this case however with all of the numerous things to do in Vienna, I feel like time could be spent better elsewhere. Here’s why:
Kreuzenstein Castle is located less than 30 minutes from Vienna by car (which a little more than doubles when using public transportation). During my trip to Vienna, I did not have a car and relied solely on public transportation, which means that I had to take the train to Leobendorf – Kreuzenstein (approximately 30 minutes from Wein Praterstern on the eastern edge of town) and then walk 40 minutes through a combination of streets and woods.