What should I do about a bad drywall job on the ceiling?
The usual approach is indeed to scrape to a sensible point and respray. If you're going with acoustical texture again you don't have to skim first if it comes off fairly cleanly. 

You can rent a texture sprayer and do it yourself. Practice first to be sure you have a suitable mix and an understanding of how distance and pattern will affect the outcome. 

Above all, start thin and build up. More texture is not necessarily better texture, and you can't take it back once it's on there. :)