Is there a point in requesting a seat on a plane before check in opens?

Unless you have a specific preference and are willing to pay the extra, I would not. Haven't flown British Airways but this sounds like just an airline scam to get needle the customer for more money. Most airlines in US let you select your seat (for free) at booking. Of course, some airlines have seats with more leg room and they may charge for those. I would not pay the extra myself, especially since you are flying alone, and just request an aisle or window seat (your preference) when you check in.