1) There is immediate science value in getting a detailed satellite shot of the target for detailed and ongoing ground investigation.
2) There is publicity value in ANY shot of a landed or chrashed craft (I agree with your point here)
3) It is easy because WE KNOW WHERE OPPY IS

Without item 3, we're looking at a major ground search for an uncertain shaped target. The less that is known about the EDL trajectory and event sequence, the less the final target is known.

Be aware that we know where Oppy is by a combination of space and ground imaging and radio triangulation that has been going on for a year. When it first landed, if it hadn't talked, we wouldn't know where it was in an uncertainty ellipse hundreds of km long. In the case of Beagle, where even the integrity and stability of the heatshield is in question, there is huge uncertainty in where the debris field lies, and whether there are any fragments large enough to image. MPL is a bit more certain, but still needs a wide area checked.

I fully expect that the prime target area for each of these missing craft WILL be imaged, but not as a priority, and not exhaustively. There are plenty of other science mysteries of Mars that are begging for detailed imagery.

As an analogue, would you rob Hubble observing time to photograph failed Geosynchronous relay satellites to find why they failed? Even if this exercise had subtle feedback in the durability of future space systems, it's a stupid waste of a prime science asset, imho...