Unfortunately, I don't think Playdo is interested in bringing Spineworld back. They've been e-mailed thousands of times by lots of different people, and they apparently only reply with one phrase: "We will not bring Spineworld back." I've e-mailed them myself once or twice, and never got an answer.
Personally, I think their customer support is kind of lousy. When Spineworld was still around and something happened to my account, I used their help center to send them an e-mail about the problem. It took them days to respond, and all I got was an unhelpful reply consisting of a couple of short sentences.
In short, Playdo deleted an extremely popular game without explaining why, replaced it with a similar game that is completely boring, and don't want to tell us anything.