Let me answer your questions:
"Is there safety risks by adding a lift?"
If the lift is installed correctly the only safety risk is having a higher center of gravity than the stock 4Runner. This will change handling characteristics a bit. Now, if you add bigger tires or different offset wheels you might have to do a BMC (body mount chop) to keep these from rubbing. The body mount, stock, is designed to deflect the wheel and tire downwards in the event of a crash to keep it from encroaching into the cabin. That is a concern because cutting it will mean it could not protect as well in an accident.
"Is there accelerated wear by adding a lift?"
Yes but not because of the lift. Most people who lift also add larger and heavier tires, higher offset wheels and/or wheel spacers. This can lead to accelerated bearing wear.
"Is there more maintenance required by adding a lift?"
Yes. The OEM components will provide the most reliability and durability for the longest period of time. Aftermarket components, while improving your off road performance could wear faster. Depending on component selection, your shocks will need to be rebuilt. Your UCA could need the uniball replaced, etc. More grease points, accelerated bushing wear, etc.
"Is there an efficiency loss after adding a lift?"
Yes. The heavier, larger diameter tires along with the vehicle being higher could cause a significant loss of efficiency. If you currently average 18 mpg overall you will probably lose 10% after lifting and adding wheels and tires. If you add skids and bumpers and rack you will lose an additional 10%.
"Is there going to be more problems after adding a lift?"
Probably. There are very few complaints (using the unscientific data of this forum) that arise from the stock 4Runner suspension. Most of the suspension complaints you read about here like rubbing, noise and wear come from guys who have lifted their vehicle.
Now, I have honestly laid out all concerns you could have from adding a lift. Is it worth it? Only you can answer this yourself. Some people don't care because to them it is worth it for the "look" or the off road performance increase. Those are the only two reasons people lift it BTW. Hope this helps.