As you're gold in full fare Y, you're presumably in one of the better seats and as such I'd leave it on a short flight as it's only 20 extra TP rather than 70, and only half the length of an average TATL yet the same cost.

If I were doing LHR-IAH on an O booking, I'd be all over it.

While it's not so cheap that I'd call it a racing certainty, the fact that you're being offered it at all means that you might have a shot at an op-up - though of course if you do choose to upgrade, you might find that you get a magic beep even further forward.