It should be noted that this offer is only for those that received the email in the first place, due to being a Sony credit card holder. So if you don't have the email, you can only be a referral and can't get additional credit for getting others to buy vitas. So obviously this wasn't part of some master plan to get more people to buy Vitas, but rather just a reward for those who have the credit card.
That said, I love my Vita way more than my 3ds. And I primarily bought it to be a Persona machine (P4G and P3P). If you've never had a PSP, then there's tons of awesome games and they all look so nice on the beautiful OLED screen of the Vita (which is so much nicer than the 3DS screen).
I do hope that more titles come out, but I'd say that it's been worth it. It probably won't see more sales until a price drop, just like what happened with the PS3 and PSP.