I've been working on the same libre project for more than 25 years, and making a living from it for about 15, so I have my own perspective on this.
The biggest issue that I see is that even for things that are in some respects "finished", grants on the order of $5k do not change the maintainance picture very much at all. If there's a sudden crisis with critical infrastructure, people will step. But that's precisely what we want to move away from, and to do that the funding needs to be living-wage level, not single-issue grants.
It is awesome when those grants happen, and specific new features or compatibility are worked on. But the sustainability question is really not about that kind of work, for the most part. Somebody needs to actually be the guy in Nebraska and they need to consider that their role. Possibly it is just one role among a few, but it needs to be bigger than a one-and-done $5k-sized role.
The question is really how to redirect the streams of revenue that currently flow toward capital so that the people who work on OSS can do this as a living, not a part time calling. I don't see grants as a significant part of that.
Now the Open Source Endowment is a very small organization that starts with ~$5k microgrants. It is not enough for a living but still should help maintainers not only financially but also by allocating attention.
As it grows bigger, the grant size will also grow. One can help with this by donating and bringing in new donors!
A grant can be for a lot more than $5,000. It can be for as much as the grant-making org has and wants to spend. Grants can be given on an ongoing basis as well.