I have taken a 500A Rocketeer from just about that state to an excellent functional machine. But it was a PITA, cost extra money, although not that much as my LSMG had all the parts I needed, and a lot of work.
I'd agree with Candice and Miriam, keep looking.
The cams allow the machine to produce decorative stitches. Most ZZ machines will do ZZ and SS with perhaps a hem stitch. Then there are those that have a ton of built in decorative and functional stitches. Patterns, stretch stitches, hem stitches and others.
And then there are those like the 501 that need removable cams to make these patterns. Generally the machines that depend on the removable cams are simpler mechanically than those with built in cam stacks. That is a good thing but not a necessity.
Joe