A page per service area is likely to be better from a pure SEO perspective, particularly if these relate to phrases that potential customers are likely to serve. A page per service is going to give you the opportunity to really expand on the information on offer and probably rank for more related terms further down the tail as well. It also makes is easier to focus your one page optimisation more at the theme for each page.
From a user experience / conversion perspective it could help too. That additional information, some focus and the chance to sell the benefits more should funnel more people towards conversion if it is done well.
One potential pitfall is if you are in an area where potential customers might not know exactly which product areas are right for them. The "everything on one page" approach can work well when people want to scan their eye down what is on offer and find what is relevant to them. Many sites now take a best-of-both approach: Have one page per service, but still have a services page that gives a shorter overview of each aimed at directing people towards the right choice for them, as you suggest in your last paragraph.