The rotary processor will give you an even agitation, and temperature control, depending on the model, I think, but that's about it. If you are not careful about your solutions, your exposure, your whole chain in a nutshell, then having a rotary processor will not help. You should try to identify what problem you wish to solve, and then see whether the rotary processor is the right answer.
Can you detail your working procedure a little more? What camera, lens, film, tank, developer, stop bath, fixer, washing agent, washing time, water, time, temperature, drying procedure do you use? Also, have you tested for your Exposure Index (the "effective film speed") and for a correct development time adjusted to your enlarger type?
5-7 rolls a month seems a scarce amount of film for investing in a Jobo. Plus, you do only B&W, which is less sensitive to small variations than colour is. My instinct would be to work on your development procedure before buying new gear.