I think for me, it is about finding the balance between what points I can earn or buy compared to what I would like to redeem or what is available.
As I rarely earn any points from flying anymore, the only way to generate points is via regular shopping, (the occasional credit card sign up promotion) or through the purchasing of points directly from the airline.
Earning points via regular shopping, I find that I can earn 3 SQ points per $1.00 at supermarkets (and that's where I do my regular shopping and thus do not need to spend more chasing points, also add a few more supplementary cards and my whole extended family can generate points for me

) In terms of using those points, I find SQ offer a decent amount of availability to/from Europe and they fly direct to several cities I would easily/happily fly into - so it makes using them much more convenient. Yes, the taxes can be high but sometimes you just have to suck it up and pay for it. I mean, I would love to be paying AA type taxes all the time but if I can't get a seat - it doesn't matter how low the taxes are.
The last few years I have been buying points directly from airlines, there's several threads on the pro's and con's of each program with respect to buying and redeeming points - that has been very useful too. Buying points has also allowed me to save up my SQ and QF points, and now I have finally redeemed all my SQ and QF points for a RTW trip in F for me and the +1