Fair point, I hadn't thought about the force/stress from the side stand being applied in a different direction on the centre stand. Probably would be as likely to fail, long-term, as a weld would do and like you say, it would be gutting to come back to it having a wee lie down one day.
Was hoping for a lightly cheaper repair, but needs must, I'm not too confident about the engine mount bolts being so close to the failure as well, although the bulk of the frame around the bolt is still sound.
to be honest, I think that someone has nudged it in a car just enough to start a crack/split but not to tip it and over time it's just got worse and worse. Can think of how else that would fail, not that I'm a huge bloke but even I never sit on the bike whilst on the stand etc.