ok there is a reason for market specific PRL's it not just cricket trying to crew you or confuse everyone. it is to ensure the best fringe coverage possible without customers defaulting to a roaming provider in their home area. keeps the costs down for cricket (are indirectly cricket's customers). however any roaming prl will work if you have roaming on your account (you just might roam when you should be on cricket coverage)
and no there is absolutley no point to making a corabined PRL of any sort, the only difference between the different roaming prl's is order of preferred networks (that is my understanding anyway)