Congratulations, you have demonstrated the value and made it easier to do something. As someone who has gotten promoted 2 times (and soon to be 3) primarily off of tech debt reduction and infrastructural improvements that don't themselves do anything, but drive future productivity, of course I think this is valuable. This kind of thing is literally the only work I do.

Now yes, there's a point beyond which only doing that work won't get you promoted, but that point is L5 where you're making 350K/year, and you can continue to do some of that work and get promoted further, you just likely have to

1. Get other people to also do that work 2. Do other work that acts at a larger scale

If you're actively adding new features to a service, you aren't doing maintenance. You're launching new things, and people get promoted by launching new things all the time. And people get promoted for making it easier to launch to features all the time.