Ill take a crack at this though I'm going to paraphrase and ignore thousands of small details but here was my experience:
At the time we were making 40k we only had one product. As such, growth could only come from either:
a) winning new clients with the service we had as is ("sell what you have to more people")
b) adding new functionality we knew our clients would be willing to pay more for ("figure out a way to upsell what you currently have") or
C) create a new service altogether that you could cross sell ("find something else to sell them")
We did a combination of a and c.
Strategy A is clear-cut. If you want to make more money go find more people to buy what you have. Of course, this is easier said than done. Is your solution any good? Is the problem worth solving? Is the lifetime customer value sufficiently higher than your customer acqusition cost? All of these things play a roll here. For us, I think all of the above were true. Our biggest challenge is we sell to enterprise and financial services at that which requires a robust outbound sales process (in other words, no one is going to sign up for our tools because of a twitter post or mention in a news paper). The key takeaway about this is that to grow a SAAS solution, you need to be thinking about how you are going to sell it from day one. Internally we are constantly asking ourselves "how do we merchandise this?" (I realize that is not the best word but it captures a lot of things you need to be thinking about). We don't initiate development of any feature or product without seriously considering and designing a sales strategy around it.
Strategy C (cross sell) is worth highlighting here. I believe people mentally don't like paying more for the same service once they have been anchored to a price point regardless of how much value they get from it. As such, I spend a lot of my time pondering services or tools that I can cross sell. People like vendor consolidation and once they know like and trust you it's easy to get them to open up about other solutions. Because they are distinct solutions you can start the pricing discussion from scratch and command higher fees. Another huge benefit is bundling always improves attrition and can become a major barrier to entry to the extent you are in a competitive space.
That's not to say B isn't important, we are constantly innovating. I find pricing to be a bit more sticky in the SAAS space so improving a product is more about creating moats, reducing attrition, building brand etc.
Not sure this answer will help as there are a lot of "it depends on what you are doing for who imbedded in my answer".