Dan Kennedy taught me, there are only three ways to make more money:
Sell more, to more people, more often.
You can sell to the same person once, or once a year, or once per week, or several times per day. You can sell that person more expensive items, less expensive items, bundles, up-sells, cross-sells, down-sells.
You can find more people to repeat that process with.
Thus we can simplify further: sell to more people, and sell more to the people you're already selling to.
Most businesses spend a lot of time, money and energy (these are somewhat interchangeable entities) finding new customers. However, this is the most difficult way of making more money.
If you treat customers well, and actually solve their problems so they come to know, like and trust you, they will be naturally inclined to buy more from you. And even refer their friends.
As a SaaS, you're well situated to play on all of these strings. Recurring revenue is the name of the game for SaaS companies. So most of us already do sell to the same customers again and again. And we want to keep them happy, we are product builders and want to create great products, and we languish over churn.
We could also create add-ons, for example, for features that do not really belong in any tier, because most people don't want them, and they hate paying for something they don't use. Special features could be bolted on with premium pricing for the specific features.
We can also create referral machines. Build in ways to let our customers bring their friends into our worlds. Through affiliate programs, free courses, and other lead magnets, like calculators.