I'm one that falls into the camp of "I've paid for a J ticket so I don't want to be sleeping next to baby on board". It being far cheaper to pay for the odd seat here and there than it is to fiercely throw money at TPs and gaining free seating status. Saying that, some seats on some routes working out at £300 rtn on top of original Avios/cash layout for tickets is pretty galling; even more so that it is 99.99% profit for BA.
The plus side, on occasions I've done a dry run booking including paying for seat reservations only to realise it is cheaper to fly in F (with free selection) than it is to fly J (+paying for selection). Add in CCR consumption on these bookings then I like to think I've helped reduce it to 96.99% profit for BA.