Because the BA website will only show you the seats that are currently available for you with your status, it's worth having a look at the seat map on Expert Flyer (download the app and you are able to do this for free) as it will show you what seats are actually booked, and which are simply blocked. If most are showing as booked, you may think it's worth paying the reservation fee - if there are plenty that are just blocked then hold on until check in opens (although there are no guarantees that blocked seats will open up if it's not a busy flight).