If a buyer has to pay a fulltime developer to replace you guys, then your business wouldn't make them very much, unless it keeps growing for a few years without cost increases.
The product can fit well into competitors portfolio of products and can make them much more than what we do (they are established, big, have sales channels, etc)
For example, if you commit to stay on some number of years and an exciting opportunity presents itself during that time, you want the compensation to be enough that you can pass on the opportunity without too much heartache.
Sounds to me like it's time to trade up, get a smaller piece of the bigger pie. Ask for cash + equity swap. Get some ownership in the parent organization.