BA's IT is the source of much frustration here. Many people don't rely on it to do anything automatically, even when it's supposed to. If you do anything even slightly out of the ordinary, it's useful to expect it to go wrong and to have to ask for it to be sorted out afterwards. (Personally, I don't think that the IT is actually that bad, but things do go wrong sometimes.)

Whether an effective cost of £59 is worth it is always a matter of personal judgement. In your case, you're not getting any lounge access that you wouldn't already have, and while there'll be a few extra Avios, in effect there won't be any extra TPs (other than adding a tiny bit to your lifetime total). But you will get to pick your seat, FWIW, which you can't on your current HBO fare. I think I would do it, and I would definitely do it if my companion were travelling (whether with or without me), but there are certainly other people here who would perfectly reasonably take the view that that's sixty quid that could be better spent elsewhere, eg on a good meal in Venice.