If you use a simple process of how much do the points cost to get, compared to how much spend would whatever the cash fare i am willing to pay equal and if the points (plus taxes) come out lower then you are getting 'value' out of the points and benefiting by accumulating them, if you did the sums and the points (plus taxes) come out higher cost than the cash fare then you are putting money in the pockets of some airline/bank etc (which is what they want)... The cost and benefit go together to equal value (or not)...
Once you have done the sums it at least gives you ball park averages for you to work with, you can then redeem for something that isn't value with the full knowedge that your making a conscious decision, most people have no clue of how to work out a ball park average and make decision after decision in ignorance... As they say knowledge is power and I like to have as much of that as possible....
Anything roughly over 1 cent is also the cost at which i will stop attaining points as I can't predict the future and while yes J class redemptions currently will almost certainly be valued at more than this (and so its a sensible investment if you can find them to where you want to go), it gives plenty of wiggle room for taxes and surcharges to go up and devaluations to occur and they still have a benenficial value... It also allows for some quick calculations at the shop, paying bills, comparing between programs or when applying for something rather than ascribing them some 3 decimal point value...
Once again, adjust it for your own circumstances and aspirations and if you like donating money to big businesses (especially the trick of no activity in your account for 18 months...)