Hi Ann,
From my view, there are 3 ways to serve a company.
* write copy
* provide marketing consultancy, and
* provide organizational/procedural consultancy
That third is 'project management' (in board market terms).
As an Executive Assistant you probably don't deal too much (directly) with copywriting or marketing, which means project management is likely how you might best serve the company.
Which is good for you because project management is a high value / big market place.
If I were you, I wouldn't waste my time getting a silly piece of paper that says, "Hey, I'm certified". I'd simply upgrade my organizational skills to meet the requirements, as per the demands of the job.
I highly recommend two places for getting organizational skills:
#1: http://www.organizedlivingworld.com
#2: http://www.web3Efficiency.com
The second site is more for personal productivity where as the first site will probably give you the most benefit in terms of getting organized and being successful in the corporate world. You'd probably do well to subscribe to the RSS feeds for both.
I expect this might help you in some aspect Ann.
Highest Regards