I have a lot of experience of public sector projects and all have used Prince to a greater or lesser degree. I can't remember anyone having formal training beyond the 2/3 day introductory course.

If you want to work on government projects (if there are any in the next few years) it would be very helpful to understand the basic framework of Prince and the most widely used terminology.

If you are an experienced project manager you'll recognise most of it, though Prince may have different terms and is more formalised. I wouldn't recommend spending alot on training courses unless you are sure it will be required to get employment.