Microdermabrasion will do absolutely nothing, sorry. Actually that's a lie, it will make your brown spots/pigmentation look darker. Why? Because microdermabrasion takes off only the top layer of skin. The pigmentation/melanin is produced much lower so by taking off the top layer you will be able to see the pigmentation problem a lot more easily. Obviously that's somewhat temporary as a new layer of skin will eventually grow back.

Sorry to be the bearer of bad news. I've tried microdermabrasion for this exact problem. Doesn't work.

Something that's about the same price and DOES work? Pumpkin peels! I have fallen in love with them. If you're serious about getting rid of pigmentation you need to have a peel once every two weeks, for about 8 weeks (so around 4 peels). Being a peel you'll be flaky for 3-5 days afterwards but man it's worth it. Active acne? ZAPPED! It's truly awesome but you must find a qualified and trustworthy technician to do the treatments for you. You cannot be left alone while the treatment is in progress so if you do go for it then make sure you suss your clinic out well.

Good luck!