Analise,
We all have a favorite airport where we'd like to see a PC. And we can always come up with lots of good reasons why CO should put one there.
For example, SNA. High volume of traffic, lots of business flyers, and due to demand, tickets are generally more expensive out of SNA over LAX. Even the leisure flyers are well-heeled. And lots of NW, HP, and AS flights go out of there as well. So a combined CO/NW/HP/AS club could certainly be justified!
Ditto with SAN. And from what I understand CO was going to put a club there, but then dropped the plans.
These days CO and other other airlines are reducing hours and closing clubs. So expecting them to add new clubs is a pleasant thought, but just not realistic.
EWR-COflyer,
I realize that PC's aren't put there to draw the locals. But you have to consider how many CO flyers travel through that airport. At MCO, CO doesn't have a big presence. US and DL are the big players there, and UA is a big player just about everywhere. So they have clubs there, while CO doesn't. TPA is much more of a business destination than MCO. But CO doesn't have a club there, either...but US, DL, and UA do!
OTOH, CO has 4 PC's at IAH for one simple reason...most of the people flying in and out of IAH are flying on CO, and a lot of them are PC members! But just try to find the US, DL, and UA clubs at IAH!

CO puts their clubs where they have a large volume of
CO flyers who have a high probability of being
PC members.
Your idea of swapping day passes is a pretty good idea though. Or at least it was until CO reduced the passes in our Elite packs to one, and put an expiration date on it. I've swapped a couple for AAdmiral's Club passes which I can use at SNA.
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"Read my lips! No more benefit cuts!"...Gordon Bethune