The answer to this question depends on a number of factors, including:
When we look at solar power in raw financial terms, then a few factors come to the fore:
Existing electricity supply:
If you are already connected to the grid, then solar will take a number of years to pay for itself. Solar has a high hardware entry cost but very low ongoing costs. The initial cost is falling rapidly however. An existing connection to the grid has no entry cost but much higher ongoing costs than solar (as you are paying for the power).
However, if you are not connected to the grid, solar is much more attractive. It can cost in the order of tens of thousands of dollars per km to connect to the grid. Not a problem if the powerlines run past the front of your building. A big problem if you are a few km from the power lines. Solar suddenly pays for itself much more quickly when compared to grid costs.
The amount of energy reaching the ground from the sun depends on location. The sunnier a location, the quicker solar power will pay for itself. If you live in a low sun / high rainfall area you won't get that much power from solar - it's unlikely to be worth it.
Solar power is much more viable when integrated with other solar technologies. A building that uses passive solar heating and water heating requires much less electricity. If a building loses less heat, it needs less put in from energy inefficent heating.
A well insulated and naturally lit building also has this advantage.
In many cases, this means solar can work better with a new building, designed with energy efficiency in mind. This certainly doesn't rule out the use of solar with old buildings.
Integration with energy saving measures just means that reduction in inefficiency will see solar paying off much sooner.
Cost of hardware:
The cost of a solar power setup depends mainly on how much power is needed. Other factors such as difficulty of installation and the need for customisation do come into the equation.
If you need a lot of electricity, the inital cost of solar will be very expensive. On the other hand, once installed, the savings compared to paying for each unit of electricity will also be high.
For many people, using solar power is not primarily about money. Rather it is about reducing the damage we do to the enviroment.
Worth is based upon what outcomes you value and how much you value them. If the only outcome of value in solar electricity generation is financial benefit then solar only needs to be evaluated against the factors discussed above. If it never going to pay itself off, then it is obviously not worth it.
However, for someone who includes the outcome of enviromental benefit in the equation, the question of worth becomes a bit more complex. This may mean accepting that solar won't pay itself off quickly, or will never quite pay itself off. This is a personal choice, but is something to keep in mind when looking at solar.