I'm not a master gardener myself, so take what I say with a grain of salt. That said, I think that if you're willing to put in the work, both the title and the training you have to go through to get it will be useful. You take real college-level courses in botany, biology, horticulture, etc. The information is valuable, plus higher education in your field always makes your resume look better. The volunteer hours will give you more experience working with the public, if you need that. And if I ever had the kind of lifestyle where I could even begin to think of having a "personal gardener," I'm pretty sure I'd be impressed by an ad with the words "Certified Master Gardener" even if I didn't know what it meant!

HAVE YOU TRIED CONTACTING YOUR STATE'S GOVERNMENTAL WEBSITE TO SEE WHAT PROFESSIONAL LICENSES & TRAINING ARE REQUIRED FOR THOSE PROFESSIONS, & TALKED W/ PROFESSIONALS ALREADY IN THE FIELD ABOUT THEIR JOBS, PRO & CON (RESEARCH INTERVIEWS)?? ALSO CHECK OUT THE REFERENCE LIBRARIAN @ YOUR PUBLIC OR JR COLLEGE LIBRARY,AS WELL AS ANY LOCAL GOV'T VOCATIONAL DEPTS...
IT'S A WORTHY GOAL, BUT YOUR EFFORTS NEED TO BE FOCUSED SO YOU WON'T WASTE GROWING SEASONS...GOOD LUCK TO YOU, K.

MAster Gardner title is impressive - to those not in the industry. I received mine about 7 years ago. Since then, I have received my ISA arborist sert and CNP as well.
It's a good start. But remember, MGs are trained simply as community volunteers - although very useful in many senses - they are hardly professional not is the training extensive. The training is merely a basic overview of a number of areas. It's pretty good though but on the low end of the scale compared to the other professional certifications.
See if your state Associations: Landscape, contractors, horticulture, etc... has a Certified Nursery Professional (CNP) or a certified landscape technician (CLT) program. These are very extensive and some of them are internationally recognized. For trees, you cannot beat the ISA Certified Arborist program.

Also, I have found that extensive, although progressive, reading, writing and research - as well as OJT and field work - have been the best teachers and lessons. I have learned more this way than any other certifications.

MG is not really a certification - simply a volunteer title. they are there as volunteers for your state's Land Grant University and County extension office. They work at the county Fairs, answer phones about tomato and vegetable insects, use countless reference books for these calls, volunteer at the local botanical gardens and community garden contests, etc...

thats what you can expect your job and responsibilities to be after receiving the MG. BUT, I do agree it's for a great cause that is funded by the taxpayer.