My old Allez had tiagra 9 speed my new focus has ultegra 10 speed - worth £500 to upgrade your existing bike I would say no, not that ultegra isn't great as I love mine but you won't feel a massive difference apart from the ergonomics which are nicer (better hood comfort and no thumb shifters for me). Would I spend an extra £500 on a new bike to get ultegra then I would say yes if you can afford it as you won't regret it.