SnGs have the same problem as cash games, which is basically the rake. If there was no rake, then I think, playing SnGs would be very profitable, because they do attract a fair amount of recreational players, who make a lot of fundamental mistakes. However poker sites typically charge around 10% in rake. And that is pretty difficult to overcome, since each game dont last very long, and there is also a limited upside potential, when at most you can get your money back 4,5 times less the rake in a traditional 9-man. So if you are going to grind SnGs, you ideally want to find a site with low rake and/or a good rake-back deal.
As for strategy we are not going to cash in every one, but for traditional 9-mans and 6-mans it is very important to cash as often as possible and be very aware of bubble dynamics. In a 9-man 60% of the price money is distributed on the bubble, whereas in a typical MTT its only 30%.
So a 9-man SnG is not the place, where we want to be a "hero" and go for the win only. As a middling stack we need to play very conservative against larger stacks and simply wait for the short stack to bust, so that those 60% of the price money is distributed already. And even after that, if stacks are very uneven, we still dont want to bust as the middling stack and let the short stack get a free payjump. Only when its down to heads-up can we focus solely on winning chips, because now it is obviously "winner takes all".