Giving up good position because of studies
An important consideration is "window of opportunity".  How long will you have the chance to go back to school?  Will the school be happy to let you defer for a year?  In contrast, if you leave your current job for school, is there a good chance that you could return to work there after you finish a masters degree?  

Also ask "What are my long-term goals?"  It sounds like you mainly want to be challenged and experience personal growth; perhaps also to "do something useful".  Do you have others long-term goals?  How likely are you to be happy and on your way to these goals in 5 or 10 years if you stay at your current job.  Grad school can be fun, but it's often just a way to delay "real life" for a few years.  If you get a masters, will that really help you to be happier with your life and where you're headed 5 or 10 years after you finish school?