its very best idea if ipb introduce New Topic / Reply Ratio system , will Minimum then Spammer and Spammer Reply .

Ratio: The ratio is Threads divided by Replies (your Threads / your Replies).
For example:

If you have 30 Threads and 100 Replies, the ratio system will divide 30 threads by 10 replies.
30 Threads / 100 Replies = 0.3

Admin can set After Minimum Ratio After it reply will allowed ,

I don’t get it. Does that assume that spam appears in replies, but not new topics? Why?

And if replies are only allowed with a specific ratio, how would one even reach that ratio? 

forexample i daily post 5 games links , ok  , user comes and just reply take link and go , but with ratio system , user will auto force for reply at 5 games link need to be post 3 , 4, 5, like any which we set new thread counts , so with this step contribution of members will increase and will make new threads fro get replys.