No I completely agree with you. I've been thinking "do I really need another pair of headphones?"...
I've been thinking that since my current headphones aren't really meant for portable-use (as in during bus commutes, listening to music at school, etc), maybe it will be worth it to invest in a more portable headphone. After all, a [slightly] bassy headphone is better suited for the portable/on-the-go/transit consumer.
If you like the M80's, I don't see a reason to spend $300 on a headphone that is essentially just a slight upgrade.