It depends on your travel plans and differ from person to person.

If your job causes you to sit for hours in public airport lounges, then the answer is yes. If you alway travel with a particular airline or with oneworld/staralliance airlines, then it may be better to build up status that way. However, it you fly on regularly various airlines or budget airlines then maybe it is worth it. I get mine with my credit card (no it is not Amex Centurian) (two actually - one for me and one for the supplementary cardholder) so it is a convinience. For the ad hoc trip, it is possible to purchase access to various lounges which coincidentally normally the same lounges that priority pass gives you access to. Just trawl through on the internet.