As others have said, it will really depend upon your needs and your goals whether it is “worth” investing in a personal 3D printer.
To add to what others have said, my opinion is that, for most people, there is no great benefit to owning a personal 3D printer. If you are a hobbyist and enjoy tinkering, or if you have a particular and recurring need, then maybe it would be worth owning your own printer.
However, most “desktop” printers can’t really approach the accuracy, speed, or materials available in “professional” printers. Just like owning a car, it can be expensive and time consuming to keep the printer running.
A big argument against the value of owning a personal 3D printer is that, for most people, it would be far simpler and more cost effective to take advantage of a 3D printing service whenever you need something printed. Unless you expect to be printing stuff all the time, your money would be better spent getting better prints from a professional 3D printing company that has access to professional-grade machines.
As others have mentioned, another thing to consider is that 3D printers aren’t really all that useful unless you can create printable CAD designs. There are online services (like our company, Cad Crowd) which offer both CAD design and 3D printing services. For most people, that’s probably a better use of resources than owning their own printer.
Of course, as the technology progresses and the capacities of desktop 3D printers improve (and the cost goes down), this equation could change. For now, though, most people would probably be better off taking advantage of a 3D printing provider.