yeah, im going to sound like pervy mcperverson by the time im done here, but when it comes to public/outdoor type shows it is much like has already been said. when it is new, it works really well, after the first 5 times or so it doesnt. the exception seems to be niche markets. i know of one model who does shows at work, while the office is full of people, and does it in such a way that it always feels like something risky and dangerous and exciting. and of course if a model is known for doing this type of show her personal following of regulars may be able to keep her going as fetishists tend to be pretty damn loyal folks.
the new/ old dichotomy seems to hold up on a per model basis though. any given model can do one if she hasnt before and will probably make some serious bank if she advertises well or has a large following anyway, but without upping the ante each time the returns diminish.
from what i have observed and noted (though my notes on it are illegible as hell and only about a third of them make sense) up to three shows is the magic zone where good token flow occurs, as long as it isnt done three days in a row. if spaced out over a few weeks it could probably be stretched to 4 or 5 shows before tipping started to nose dive.
as best as i can tell looking back over my data here the optimum rate for a non niche model (one who doesnt do "only" or mostly public type shows) is to do them no more often than once a month. i've got 3 listings where over 15k was made in a 3 hour show, for 6 shows over a period of 6 months that way, and then i lost track since i took a break from MFC and any other cam sites at all for a year or so and lost contact with the ladies who were helping me back then. i dont keep records any more since i abandoned that novel so all of that is about 2 years out of date, but it probably scales ok