A colleague and I have just sat down and pored over some thrilling pension information. We discovered that if you are interested in buying extra years in USS you only have till 29th Feb to ask for a quote. This is the same whether you are on the old fogeys final salary or newer academics average salary schemes.
I started buying extra years when I joined USS because I realised I wasn't going to accrue a full pension otherwise having started my first academic job quite late and because my dad told me to.
My DH works for a government department with a similar pension scheme and he thinks it's a bit unnecessary (I started before I met him) but I'd prefer to be a bit independent and he admits that USS is a bit less generous in other respects.