Strength of squad is obviously important. if some squad has more strength than all protour squads, it's going to look very odd. it should be the most important criterium.
I'm going to add another criterium: age. how long has the squad been in the peloton? how long has it been there on a high level. this is important because nowadays sponsors don't really stay very long, so teams don't have a fanbase. cycling is something you can do for two years to give your brand some appeal and then you get out of it because, hey, it costs money (Cervelo). those that do stay for a long time (like rabobank, eukaltel, lotto) should not have a hard time getting a license.
financial stability is also important, of course. But I would not really put a prime on it. sponsors would just cut budget in order to be more credible. besides, with dope nearly eliminated, what else is there to make a good newspaper story?
cleanliness is important, too. But I wouldn't say 'Hi Liquigas, last year one of your main men was caught. So you are out'. or 'Hi RS. your icon is under investigation. now you cannot ride the vuelta'. that stuff belongs to banana republics.
I would rather install a very harsh rule: one doping case and you are out of protour for a year. that will make the teams work reaaaally hard to archieve it. and the riders would, no doubt, work hard too (it's one thing if you get caught, but if all your mates get caught too, that would make you think twice). only next year I would start enforcing the rule. i.e. if Rocketboy riding for Dopesquad was caught in '11 with too many fireworks in his behinds, then I would boot Dopesquad from the protour for '12. then they could re-apply for a license in '13.
global appeal is something I don't care about when it comes to handing out protour licenses, it's more important when selecting protour courses. if all the great cycling teams come from Italy, then so be it.
"Big Star" attraction? usually if you have a big star, then your squad is strong enough. it should not be a criterium.
'Ability and desire to challenge throughout the year'. whatever. not important.
development of talent? not important.