You are right not all sites indexed with breadcrumbs show breadcrumbs in the SERPs - here is Matt Cutts take on this which might be useful for you
- http://www.youtube.com/watch?v=PmOjX5DlN2A
I would put together an example of a few top preforming sites that are leading the way in e-commerce that have breadcrumbs in order to support your argument. It is hard to comment on whether your site looks good. Your client must remember that a good looking design is important but not at the sacrifice of usability else your customers will soon go else were as you will find it is all about how quickly and easily they can access the information they are looking for. If any parts of your design hinder this you will soon know about it...
Is the site not likely to preform as well in the SERPs - well Google has integrated them for a reason - improving their search results. On a very basic level you will have more information against your listing - including extra links so this is likely to aid the user and encourage them to click on your result.
Breadcrumbs are essentially a form of rich snippet and they add value to your listing -
http://support.google.com/webmasters/bin/answer.py?hl=en&answer=185417&topic=1088474&ctx=topic
Also one other thing is that breadcrumbs don't have to be in a massive bright font from a design point of view. A smaller grey font in a white space above the product(s) can work just as well and get listed. If you do a search for products you will see some well known sites use this tact..