OK, it sounds like you're looking at the costs to the network as a whole, rather than the cost to an individual node.  Indeed this cost will be higher (cost/node * number of nodes).  

However, the table I originally posted specifically addressed the cost per node. Here's a new one where I've estimated the cost to the network (blue column):



So...which is the important cost?  In my opinion, it's the cost per node.  As a node operator or as a miner, I only care how much it costs me.  If my actions can effectively charge the spammer $1200 while costing me a few pennies, I'll do it!  Whether a thousand or a million other nodes also contribute a few pennies to penalize the spammer makes no difference to me.  

How are you looking at the issue?