By which I mean, do they really increase footfall and drive interest in company products?
These discussions around sexism are usually predicated on the assumption that they must do. Of course, not every person that attends a trade show is the stereotypical "lonely businessman". Some of them will be happily married men for which this cheap ruse in not effective, whom may look down on the practise and may form a negative opinion of the company / product. Increasingly some of attendees will be women, whom I would speculate are rather more likely to view the use of "booth babes" quite negatively. At the very least, using booth babes looks like it might be a trade-off between a small attractive effect on some people and a larger repulsive effect on a (growing) few.
Reading that the modelling industry is moving towards making booth babes wear less at trades shows sounds like the tech industry is getting locked into a stupid "arms race" where companies compete to have the 'sexiest' exhibitors. Whatever happened to having the best products?