@Panelmember
Like you, my LEA allows parents to join as many waiting lists as they want, but I can see the logic of limiting it to a certain number. Waiting lists are already too long in many cases, and having parents pushed further down a list by someone that doesn't particularly want the school but just happens to have greater eligibility under the admissions criteria seems a little unfair.
Then again, whilst I can think of some exceptions, most parents I have encountered at appeal have been fairly coordinated in their efforts to get into a specific school - not many have simply "spammed" the waiting lists of every school in the borough.
For my LEA, I think imposing a limit would be unnecessary at present, and would probably simply make a number of people angry.
@The3Bears
I understand your frustration towards the sibling link admission criteria. In fact, it is a common complaint I hear from parents and, to some extent, I sympathise. That said, even when parents have multiple children at the same school, the first child would have had to have got in without a sibling link - relying purely on other admission criteria or the tie-breaker (distance).
But all that aside... I entirely understand your desire to appeal in the face of overwhelming odds. Parents are often put in a very difficult situation when it comes to admissions, often feeling that they had "let down their child". I don't know your case very well (only glanced through some of the previous posts), but all I would say is that don't ever lose sight of the bigger picture. Think about other options and try to realise that 99% of children do fine, even if they don't get their preferred school.
Good luck no matter what you decide to do...