Well really, no matter what you do, you have already caused ripples which have produced a butterfly effect and changed countless of people's lives without you even trying. Just the fact that you were born has probably changed the fate of mankind. So you really don't need to leave a legacy... just try your best to do good in life.
In the end, I think it's the price. $250 is more than Mommy wants to spend for her child. Bring it down to about $175 or lower and the thing will start selling. Personally, I'm enjoying my 3DS. The future titles look promising. Sony still has to prove they can make a good portable experience, because I bought a PSP last gen and didn't use it nearly as much as my DS, even though it had much more extra features to offer. Hmmm... kind of like this upcoming gen.
I'll probably end up with both since I have a 3DS already. So far, it has been disappointing because all the good software is still a ways off. But, by the time Vita comes out, the 3DS will already have a solid foundation. The Vita looks very promising, and if Sony delivers exactly what was promised, it could easily be the better of the two. But for now, I'd give Nintendo a slight edge. Historically, their handhelds always dominate, always have the best software and support, and Nintendo's first party titles alone are worth buying a 3DS for.
Honestly, sometimes I do get a bit upset if someone I know well and thought I had a decent relationship with deletes me. But I've also had the opposite happen, where I've deleted people who I thought weren't real friends, and then they'd message me asking why I deleted them. Then I'd feel guilty and re-add.
Facebook gives you a window into your 'friends' true perception of you at times.