Is combinatorial novelty without insight useful? Who cares if we're the first to use tool T on problem P?

Is this valuable to science? If so, why?

Because it leads us to understand if tool T works on problem B. How big the "insight" that we gain from this is depends a lot on how different T is to other tools that have already been used on B, or, conversely, how different B is from other problems that T has been applied to.

The range here goes from "it is mind-blowing that T could work on B" all the way to "meh, everybody knew that T would work because we use it all the time for B' anyway" - although I will grant that most works following this schema in practice end up more on the rather incremental side of things.

I think this is difficult to answer in general. While it is probably not very valuable to apply random technique A to random problem B, it is also useful to find new ways to explore existing problems. Sometimes this "insight" is just that a tool from some other domain might be used to generate additional insight. For example, finding a new way to prove an old theorem in mathematics is often (not always) valuable as the new proof may, itself, offer insights.

So yes, valuable. So no, not so valuable. But it depends. It would be valuable if it helps other researchers get more insight into a field in general, not just into the problem at hand. But throwing stuff at the wall to see what sticks is just throwing stuff at the wall.

I think your gut impression is likely correct. If P and T are relatively well known than there is little value (other than for a new student in his learning) in applying one to the other. For instance, using sophisticated crystallography software to solve a crystal structure that was already done correctly using direct methods.

I am very much a fan of datapoint science. But ideally, you can do something new (make a new compound, find a boiling point, do a correlation of response to a medical treatment, etc.) In other words I am fine with "stamp collecting". But T on P sounds a bit weak. There are so many cool things to look at, you would think these guys could get a little more novelty (even moderate things).

I'm even sympathetic to some "negative" results. But it sounds like these guys are milking things. And then the gushy wording...but don't get me started on hype scientists.

I think you have the right instinct. I would just try to figure out something a little bit more interesting. Doesn't need to be discovering gravity. But in your own work, do a little more.