Jason Fried has a good reason why you should ditch your free plan
“… The majority of the revenues for our products come from people who sign up for the paid versions upfront. So we definitely have people upgrading from free to paid, but the majority of people who are on pay started on pay... of course, more people are going to pick the free version and stay on the free version, but if you’re looking to get paying customers, ask for money upfront and you’ll have a lot better shot of getting them.”
- Mixergy Interview @ 6 minutes This isn't anything new, and is a huge problem most businesses offering a freemium model face. Before ditching your free plan you should (obviously) evaluate for yourself what is bringing in the money. If there are little to no upgrades from free to paid then there is a good chance you are not distinguishing the two enough, not offering enough added value on the paid plan, not doing a good enough job driving your free users to the paid plan, or that you need to limit the free plan in a different way. You can also stop offering a free plan and use a paid trial at a reduced cost or even $1, or just offer a no hassle 30/60 day money back guarantee.