hm, definitely an interesting idea, though I'd say that subbing to series you like and receiving Thank you posts from them on your wall is almost the same thing in a sense.
Tapastic walls definitely feel like more of an interest board than a place to write status updates and walls do tend to get generally ignored. Posting news and status updates in episodes and creator descriptions tend to be seen more than wall posts.
I present to you, probably the better way to cross promote series are to make guest comics, collab episodes, crossovers, and more comic jam type projects where it gets posted in a series than a wall post.
However, every little bit helps and a simple effortless thing like posting comic recommendations in a wall post couldn't hurt, for sure.
