Most of my revenue is coming from customers I get from Google organic searches; should I dedicate more time on SEO to further increase my revenue?

I use UTM parameters on all my links to track revenue sources, however, I see from my data that a majority of my revenue is coming from a 'blank' source which based on my analysis I think this is Google organic searches. I don't know why this is coming up as 'blank' because with all my advertising channels I always use UTM parameters. The only check I have to seeing what 'blank' is that I ask a "Where did you hear about us?" question during signup and a majority of users enter in Google; so this is why I believe this is traffic / customer leads is coming from organic Google searches. Should I then be dedicating more time/money on SEO instead of my other paid advertising methods since this seems like the channel that is bringing in my most revenue?