I don't think "treading water" accurately describes the success of the 3DS. It's doing pretty well.
3 of my friends own a 3DS, and another is planning on getting the XL. One of my friends owns a Vita, and at least two or three others have expressed an interest in owning one, if it was less expensive and had more games. We are all over 20, and in spite of the fact that most of us own iOS devices, we have very little interest in iOS games. I think the market is still here, the Vita just hasn't managed to appeal to it enough yet.
Keep in mind just a few years ago, the DS was easily clearing 500k-600k in a month like July with no real big game releases. Now Nintendo's got really work to keep sales hovering at about 130k-150k/month outside of the holidays.
You and your friends are the minority portion of the market, you may want to accept that.