Is Search Engine Optimization worth the time?

It depends how badly you feel the need to publicize whatever it is you’re publicizing. For some people, no amount of time spent working on SEO is too much to outweigh the gain of a better ranking. It depends on your business model, I suppose.
…and how well you think you can pull it off.

only if you wish to attract visitors through search engines.

It can make all the difference in the world.
As long as you use real experts, and not scammers.

Yes, it can help you attract more visitors and sell more products.