As others on this page have noted, the simple past (devalued) and the present perfect (has devalued) appear to produce the same meaning in your example. So what's the point of having different tenses if they do the same thing?
The answer is that they don't do the same thing.
We can use a linguistics concept called grammatical aspect that (some argue) is very prominent in languages such as Koine Greek but is seldom brought up when talking about English.
The idea is that when filming a scene, you can have the camera follow a character as they move around the room (close proximity, 'imperfective' aspect), or you can have the camera set on a wide-angle lens in one spot, taking everything in without panning or zooming etc (distant proximity, 'perfective' aspect - "perfective" here has nothing to do with the "perfect" in "perfect tense"). Both are viable ways to film a scene, but each gives the scene something the other doesn't. Regardless of which style you choose, the actors do the same thing; the facts remain the same. It's the feel that's different.
The difference between the simple past and the present perfect in your example is similar. The 'facts' are the same: both convey the same message, but the feel is slightly different.
Wikipedia has this helpful comment:
Aspect can be said to describe the texture of the time in which a situation occurs, such as a single point of time, a continuous range of time, a sequence of discrete points in time, etc., whereas tense indicates its location in time.
If we analyse your examples using grammatical aspect, the simple past has a perfective aspect and the present perfect has an imperfective aspect. "It devalued" collapses the whole of the past into a single snapshot, where the focus is not on the devaluing but the simple fact that it happened. The present perfect, on the other hand, conveys more of the sense of the passage of time. "It has devalued" is like the camera that follows the price from when it was high to when it is now low.
We can see this difference in feeling a bit more in the following pair:
- We fought. We won. (Simple past, perfective aspect, 'summary' feel.)
- We have fought. We have won. (Present perfect, imperfective aspect, flow-of-time feel.)
Summary: there is a difference in your examples between using the simple past and the present perfect, but it is very subtle. If both versions were uttered in a speech, it is likely that no one would have noticed the difference. But there are times, as in my fight/win example, when a writer or speaker can keep things clinically factual or bring their audience with them, depending on which version they pick.
