Please don't take any of the following as advice against getting a degree if you think it's the right thing for you. There ARE doors that are closed until you have that peice of paper. Sometimes for good reason, usually not. There are a couple guys on this board that know the math of control systems like the back of their hand, and use it regularly. Most of the rest of us don't, although there are times that maybe we should. If you're getting the degree because there are things you want to learn, go for it,
However, if you're getting the degree just for job prospects, I'm not sure it's needed. You/we are fortunate to be in an industry where a large portion of the "controls engineers" worked their way up from the trades. My manager has an associates and a boatload of experience. That's all he needed when he came on board. Unless you've been looking around and seen that you've missed out on opportunity because you didn't have the degree, you might not need it. If you do need one, an associates might be sufficient, you might not need the full bachelors.
I'd agree with others that say that an EE type degree probably won't help you as much, even if it's probably the one most people assume you'd have. I think you want a degree to help you understand the process you are controlling. My ME degree comes in handy a lot, when the main systems I'm controlling are either temps or a mechanical system powered by a motor. ChemE's are very common in the process world.
For the interviews I've sat in on, the degree/college experience has only come up when the employee was entry level. Otherwise, it was perhaps a filter, but the job req usually says degree or equivalent experience. Can you do the job, and can you prove it? As long as you can get past HR, you'll be fine.
If you have trouble getting past the HR filter, then the degree might help. However, it usually means you're just going around applying for openings, which isn't the best way to do it. The more successful way is to bypass HR and use your network to find openings where you can apply to the manager directly, if you have the contacts to pull it off.