Let me explain a bit more. I don't suggest raising prices for early customers who are receiving the same product they signed up for originally. They can stay at the same price, which is grandfathering them in.
More typical though is Customer 1 signs up in 2015 when the product had features AB. Then in 2018 the product adds feature C. Is it fair to raise prices on them? Maybe, maybe not. In this case, I would still recommend today doubling prices for all new customers. You can go back to Customer 1 and say either:
1) we raised prices, but since you are an early supporter you get the current price for life with features ABC (if feature D is added, don't give it to them for free, they have to upgrade to the new pricing).
2) we raised prices since adding feature C is providing more value, but as an early supporter we are going to keep you at the original rate for 1 more year.
Definitely double the prices right now. Since there is a free version that is generous, it won’t be “selling out”. I’m sure it felt right back years ago, but think of how much the product has improved since then. You can grandfather all current customers in (or just a year) if it makes it feel better.
I am impressed by that video from 99designs. How much did you spend? Do you have a link to their profile?
And while you're here, have you read Joseph Tainter's "Collapse of Complex Societies"? He is a very underrated thinker in the lack-of-progress area you've shown interest in.
I've been using Stripe for several years and love it. Switching to payment intents this year was seamless.
One thing I'd love you guys to do is create your own QuickBooks connection app. Most companies offer their own - yours is through Sush.io with your logo and bad ratings. I can't get it to work and I'm not the only one.