you can save much , like you have own root do whatever you whant when you without be forced to open tickets with reseller company and etc..., own settings own root , settings etc... and maybe option to backup (not all hosts provide backup)
As far as speed increases are concerned it depends on the hosting provider. If they are using horribly oversubscribed machines then you can expect really poor performance. If they do not oversell and take some pride in their services then you can expect quite an improvement.
Most virtualization systems will schedule the CPU fairly, and this can be a big advantage over shared hosting. Typically you can use all the CPU if it is available, but even if everyone is trying to use the CPU at the same time you will have a guaranteed allotment.
A good VPS can be found for very little outlay, and without a long contract. If you are unsure if it is worth it just try one out for a month.
Blue Room Hosting - High availability UK VPS KVM Plans - Multiple OS support. Virtual console and CD drive.