Thanks for the replies - I should have posted an update myself by now, so here goes.
I looked into getting the holes patched, along with a partial respray (blended in along the lines), and was pretty convinced that the sprayshop I went to would do a good job, but at around £300, with no guarantee of a perfect finish, I decided against it.
Instead, I started researching compatible badges. The most obvious was the S-Type, but as "The Voices" mentions above, the badges state the engine size (or "supercharged"), none of which apply to my 2.7 diesel! Finally, I found that the old XJS had a badge of the right size, and with the same hole pattern. I managed to track one down on eBay, though it was missing the "cup washer", which took a bit of finding - finally getting it from the USA! Must admit, the installation was fiddly to say the least, but I'm pleased with the result.
I reckon I can live with it - I would much prefer nothing at all, but when I do have a spare £300, I'm sure there will always be something more important to spend it on car-wise, so I can see it staying as it is now. I certainly prefer it to the leaper - though in hindsight, it was a handy guide as to roughly where the end of the bonnet was! :-)