Do you think is a solution to spamming? My feeling says no.
Discussion
I think it's part of the picture. Spammers are going to spam though and so long as there's free and open relays and clients that allow unfiltered content (I can't see either going anywhere anytime soon) it's going to continue.
The client I'm building has some other options for filtering, and I'm sure others are doing similar. You can require a certain amount of proof-of-work (see NIP13) on any notes/messages that come from people you don't follow. That adds a cost for a spammer to create thousands of posts that will actually get through the filter, but is a trivial amount of work for a single note or other event. The client itself also adds PoW to your own notes.