On the subject of who spends more at the airport: business pax or leisure?....
As a weekly business pax and a fairly frequent leisure pax too, I would agree with most posters here that it is the leisure pax that spends more. On a business trip, the plan is to arrive as late as possible, either go straight to a lounge if I have a business ticket or I'm on Star A or buy a cup of coffee if not. That's it. Same with most of my friends who have to fly for work.
When I have my leisure hat on I arrive earlier and have a bit of a look around and whilst not being tempted by special offers on some D class celebrity's latest nosegay, I am likely to spend more.
However - whereas leisure pax spend more at the airport, business pax generally spend more on their flights - and that is why the airlines and aircraft are there - yields/profits not numbers of bums on seats. And this is why business pax are important to airports even though they don't spend the cash in the shops.
Also can I bust a myth here: having been lucky enough to spend enough of my own flying experiences in business and first (with a lot of economy too). In my experience, first class seems rarely to have any corporate types in there, also business class itself seems an increasing misnomer as high net worth individuals seem to occupy more of these seats these days. You are far more likely to see suits in economy than in business now. Firms cannot / will not fund the costs all too often.