Although you are in a TM infringement zone. There seems to be several "myspace" keyword domain names that have sold recently, without regard for legal quandries.
looking at namebio.com we find 4 examples of sales in the last year.
Considering your 2nd choice keyword is "no" - I would say "block" is the closet in comparison to yours. BlockMySpace and NoMySpace are very similar in nature and meaning. I believe "block" although longer is the optimum keyword. I would value yours in the mid xx range. however I do see potential for development, despite the risks of TM.
My opinion would be to offload this potential headache as soon as possible!