I agree that given your current line up, the Grados will offer you something new and completely different to what you already have, helping justify getting another pair more in your mind.
Re. the circumaural thing - I may get shot down for saying this but if you're used to circum-aurals you may find comfort issues with Grados, although there are lots of options.
Bowl pads are designed to pin the ears to create a chamber between the transducer and your ear, this can be uncomfortable for some, although washing the pads makes them softer.
You can turn them backwards and they put a lot less pressure on any one part of the ear, but the foam on the back is stiff and might chafe a little (a ring of HD414 or comfie foam glued to the back might help though, I'm considering doing this myself).
You can get flats, similar in comfort to backwards bowls but a different, bassier, less spacy sound. You can cut off the parts between the slits and they get a bit more comfortable, again washing them will soften them a bit.
You can quarter mod HD414 pads forwards or backwards - very comfortable but for me sucks the vibrancy out of the Grado sound. I really don't get why people seem to like this mod so much.
You can quarter mod comfies and this is a lot better in my book than HD414 comfort and SQ wise, albeit more expensive.
You can have comfies as sold - a much derrided choice as it holds back some of the detail (but also a lot of the brightness) of Grado phones a little that many love, but I think this is underratted - Grados sound great with the smooth sound comfies give them and still have plenty of detail.
Finally, you can convert them into circum aural phones with headphile C-pads.
EDIT: Should point out that every option above changes the sound signature, so you may find yourself being dictated by SQ preferences rather than comfort anyway...