I do not think that the 150-rep hurdle of creating new tags is too high. We should not create new tags easily for two reasons:
- Having too many different tags renders tags useless for classification.
- The fact that you do not find an appropriate tag may suggest that the question is not suitable for the site. (I am not talking about any of your questions, but I am talking about a general idea.)
You should be familiar with how the site works to judge whether creating a new tag is appropriate or not. I do not claim that the reputation system reflects each user’s familiarity with the site very well, but it is good enough in my opinion.
Also, as Suresh wrote, you can always suggest a desired tag in a question. If someone with enough rep sees it and is convinced, he/she will create the tag.