Is professional detailing REALLY worth it?

The biased answer, yes. The unbiased answer, yes. A professional detailing can make your car look like it is right off the show-room floor. Pro's have a lot of skills and know-how that the weekend detailer does not really have. Also, most detailers are good at getting contaminants/scratches/swirls OUT of the paint, whereas a lot of commercial products are sold to CONCEAL the blemishes. If you are looking for someone to teach you, I am sure that a lot of local detailers will be willing to go over a few things which would enable you to do a better job yourself!