It depends on who is hiring, and since it's usually impossible to determine its profile before talking with him, it's more like a guess...
Multiple certifications/experience = bad: You are right when you say that a guy with multiple technologies and certifications can be seen as a someone not very stable.
Multiple certifications/experience = good: However, the same guy can be seen by other as a very good choice thanks to its extended experience and open mind.
It is a very personnal consideration, and therefore you can't generalize here.
FYI, I'm the kind of guy that will hire based on the second observation.
The good news
You prefer to be hired by the second one isn't, the one that will value your multiple experience ? Being hired by the first one will usually means they had no alternative.
So how to give you more change to be hired by someone that will consider what you are, rather than taking you as an alternative (with plan to replace you as soon as they get their expert)?
Be yourself in your resume