IMHO it's beneficial but mostly in intangible ways.

Just about nobody is going to seek out Frontier specifically because of the critters. However:

(1) Frontier is not a nationally-known brand like, say, Coke is. So there's benefit to publicity in that regard...fewer people will say WHO? when offered this airline as an option.

(2) Keeping the Frontier name out there is important so it remains in the minds of customers. Some people tend to shop airline sites, and if they think of Frontier they may check them out. Plus if there's too little PR, at a certain point people forget you exist or mistakenly think you're out of business or merged away. Visibility is always a challenge for smaller names.

(3) Although there's some truth to the notion that there's no such thing as bad publicity, the animals are mostly perceived as positive. Think of the type of widespread publicity Spirit gets -- it's nearly always for things like previously-unheard-of fees or blocking the recline feature of seats. Differentiating things which are viewed as positive help to increase customers' overall good feelings about the airline. The spokesanimals help do that. The cookies help do that. Even the live TV helps, because while some people may make the deliberate decision to find a Frontier Airbus flight for the TV, many more people for whom TV is not make-or-break still have a better overall impression of Frontier if they remember TV is available.

Many purchase decisions are driven by a key tangible factor....US is $80 cheaper so I'll chose them. Or I am elite AA flyer so I'll seek out AA. But plenty of other purchase decisions are driven by more intangible factors.

Let's say I'm going from AAA to BBB and Delta, Airline X, Spirit and Frontier all have nonstops at 7:00am on Airbus equipment. I don't have any particular affinity to any of these airlines, and I'm not aware of any serious fee or policy differences. Spirit's out because I've heard bad things about them. Airline X is out because I have no idea who that is. If I have no impression of Frontier (or a bad one) I might well choose Delta just because they are the well-known safe choice. But if I have any positive feelings about Frontier, it might just tip the balance their way.

Obviously real purchase decisions are a lot more complicated than the four identical options in that illustration. But anything which creates a more positive impression of the airline makes a difference. On discussion boards like this we tend to focus a lot on specific differences like someone charging $20 instead of $25 for the first bag, or a 31" versus 32" seat pitch. Many customers are not as keenly aware of the type of specifics we debate here, but they do know if they felt crammed in the last time they flew X, or they may think airline Y is old and crappy because they perceive the airline color scheme as ugly, or that the ticket counter lines were infinite when they last flew airline Y. Anything you can do to make a customer think (in a good way) "Hey, this is different" can make a meaningful difference.

It's virtually impossible to know how much this translates into increased business and revenue. And intangibles like this can be trumped by other bad things...if your planes are all filthy the customers will remember filthy planes and not clever animals. But I think there's value in stuff like this even if it's not directly quantifiable how much that value is.