It's always worth it to me to have a bed rather than an upright seat for an overnight flight, so I would certainly not hesitate to use a systemwide to upgrade from WT+ to Club on BA, if I'm not already booked in Club. As for using a systemwide to upgrade from Club to First on BA, I would say that's much more up to personal preference. The old Club World seats described above don't bother me, but I do enjoy BA First for long daytime flights (e.g. London to LA) or en route to Asia from London. So I think it depends if you might be using the systemwides elsewhere, or if you don't mind using them for shorter overnights.