Ask HN: Is it worth creating an API SDK for someone else's company?

I regularly work with a companies client API SDK and it's in fairly bad shape. The principles applied are very outdated by about 3 years.

However, it still just works...

Is it worth me, spending personal time, updating their client SDK? Is the adoption rate for something like this fairly good or will it just be a waste of time? It looks like the companies SDK was last updated about 2 years ago and now needs a major refactoring.