Originally Posted by Cymro

If booked within the promo period, it would earn triple base avios (so around 1,400 extra avios for CE or Y/B/H, vs. 350 for O/Q or 700 for N/S/V/M/L/K), plus the full base avios + cabin bonus (so another 700 or 875 of difference).

I'd value the avios at around £14 assuming it wasn't the very cheapest fare originally.
A snack/drink budget of £10 isn't unreasonable.
£30 for luggage makes a difference - and I believe that putting CE one way means that your luggage is paid for in both directions assuming that the return leg is on the same ticket.

TP value is essentially zero on the last day of your year.

So all in all, it is possibly worth doing - I probably wouldn't go for it myself apart from the luggage, and definitely not if I had an exit row (whcih I usually do, to be honest!) But it's not a complete no-brainer.

If you get your luggage paid both ways then that, plus the avios and the on-board service pays for the upgrade so I'd go for it.

Originally Posted by Globaliser

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.