Welcome to the forum Max .
Safecoin should be extremely scalable indeed. Only a few groups in the network are involved in the transaction. So it’s probably under 100 nodes that do the transaction in < 1 sec. So with 100.000 nodes in the network this ends up to thousands of transactions per second.
Could there still be transaction spamming? Yes, that’s possible, but all the transactions you make are done from your close group of nodes (Disjoint Group you are part of), so they might allow you to do 100 of them at once, but could use a timer if they think you’re making too much of them. So I have no worries here as attacks could be easily prevented with a little timer feature in the Vaults.