Welcome to FT AmeriBrit!

I think there's two parts to your question. Are Singapore Airlines so good that:
1. It's worth flying them over BA?
2. It's worth switching from BAEC to KrisFlyer?

Let me tell you my thoughts to these 2 questions.

1. If you're flying in Business or First, it's absolutely worth flying them over BA. Their longhaul Business product (on LHR-SIN) is absolutely fantastic. Service is always excellent. My only dislike is the new A380's with an all Business upper deck, you lose a bit of the exclusivity/feel good factor with so many business seats.

In Economy (which I've never flown on SQ), their longhaul products are generally rated as better than BA. Beware of discount economy fares; these can earn zero miles in Kris Flyer.

2. From a frequent flyer programmes perspective, BAEC is a overall a better scheme. Better redemption rates, better earnings etc.

Kris Flyer is useful for one thing; redeeming on SQ in Business or First. SQ are notorious for restricting redemption availability to other Star Alliance programmes. However redeeming via Kris Flyer is these days not too bad (with the new saver rates they introduced). You may find that living in Singapore gives plenty of opportunities to earn miles via credit cards etc.

A few other points:

SQ although part of Star Alliance, consider themselves special. They don't abide by all the rules (e.g. denying *G holders priority boarding on most flights).

Op-ups are extremely rare. If you were travelling in Business class on an oversold flight, they'd rather give you £1000 in cash and let you travel in Economy, than op-up you to First. They protect their premium cabins and customers very well. YMMV.

I've never been a member of their PPS Club (higher level status, entry is based on spending), but only then do you get genuine benefits (equivalent to BAEC Silver or higher - given the fact that SQ ignore some *G benefits).

Overall I love flying SQ, however I am still loyal to BA. I fly enough other routes to be able to enjoy SQ J on LHR-SIN and some ex-SIN flights, but I fly OW for almost everything else. BAEC is that much better IMO!

Hope this helps