I have used a S70 just a little bit, and find it in every way superior to my P150 of which I have extensive use knowledge. I did not find a problem with low light focusing, and I did try it in a shop once not long back when I was considering buying it and selling the P150. The other time was outdoors whenI tried someone elses's camera and there was no problem at all.My advice to you is to go and try one in a shop and look at the low light focusing yourself. There won't be a better environment!
I also query why you are looking only at the S70 and not the S60. If you aren't going to do A3 size prints the extra pixels are completely superfluous. Everybody seems to think that more pixels = better photos but in many cameras it is the opposite, with the phenomen known as "purple fringing" appearing caused by too many pixels. Up to A4 the S60 will be just as good, has the same facilities as the S70, and will keep good money in your pocket. It's like people keep comparing memory cards and writing times. How many people need to shoot at 8 frames per second I ask you?
I do print at A3 here with the Canon i9950, but then I also use a Nikon D70 for that, not the Sony. In fact I am just as guilty and in retrospect should have got the P100 instead of the P150, and as for the P200 well, we are talking overkill for normal photography. I plead not guilty because I had had my Olympus 5060 stolen and needed a camera in a hurry!