Very true Metro man. With some carriers, the 'upgradeabble' economy ticket is between the lowest and the fully flexible so it is always best to check all the options for the carrier. Also, they often change the amount of miles that are needed for an upgrade. There are Upgrades but if two are travelling, Companion seats bought with miles can be better value. I've had some very good usage out of 'miles' and continue to collect when opportunity provides.
There is a discussion forum dedicated to those collect loyalty points but (for my taste) it's way over the top. Many of the posters seem to spend money just to earn points and that is not a good thing to do. If you use the 'search' in here you will find other threads on this topic.