ooh ooh ooh, me me me! You're in luck, I just got back from a mammoth flight from Sydney to Glasgow with Asiana Airlines.
We had a stopover last night in the Seoul Royal Hotel in the Myeongdong (shopping) district of Seoul. It was all laid on by the airline - shuttle to the airport, dinner and breakfast vouchers, and the hotel itself was lovely. This is the first time I've ever done a stopover on this journey (I usually end up waiting in the airports for hours at a time for the next connection), and I don't think I would go any other way now.
It really breaks up the two 11 hour flights (Sydney - seoul, then Seoul - London)and the annoying domestic flight from London to Glasgow! I actually thought Asiana were a fantastic carrier. The cabin crew were pleasant, helpful and attentive - even after being on their feet the whole time - and were always coming round making sure we had enough water, juice etc.
SO, yes, I'd definitely recommend the Seoul option. Although Asiana provide accommodation in Seoul itself, I know of others who've stayed in the transit hotel at Incheon Airport, which is about an hours drive away from the city of Seoul.
Hope that helps, if you need to ask me anything, please feel free to ask. I'm currently still on Sydney time, so I'd best get some sleep.