I guess it all depends on what you mean by "worth it".
If you have a space where it doesn't matter about the fumes and overspray and have a respirator and there is no-one else who can be affected, or don't care if you and your family quickly become poisoned by the chemicals inherent in all paints. Then no, probably not.
Otherwise, yes they are. I built my own out of wood and it cost less than $150, and that includes the doors, fan and lights. If you aren't handy with tools, then consider that it isn't difficult to spend $35 on a kit. Only ten kits at that price will by an excellent paintbooth and respirator and give you peace of mind, and a safe place to spray paints. It's all about priorities.