Hi Amy,
I've been thinking about getting some certifications as well, so I had some thoughts about it I would like to share.
The main advantage of having certifications that you can show is that the employer can "really" see what you are capable of. I ,for example, am self-thought and that's a bit of a problem since I can't "show" on paper what I am actually capable of. So that's the added value an employer can get from seeing a certification in a certain area.
A disadvantage could be that you already have some knowledge in a certain area and you want a certification and follow classes but the classes just seem to easy, because you are already (maybe) pretty good in that area.
What you could also try, is getting a starting job at a small webdevelopers company (if you already have some experience) and then make an arrangement with your boss that you can get certain certifications on his expences, which would be good for the company...
Just proposing some things out of the blue here

Hope it helps getting together what you would like to do.