There are a couple of benefits to using a good mastering engineer, the primary one is getting a pair of experienced ears on your recordings. It goes beyond application of a Waves L2 or equivalent (although I have to say I think the PSP Xenon is one hell of a limiter and it provides dither and Katz's K metering).
A good mastering engineer won't just put gloss on your tracks, they will also provide feedback and let you know what you can do to improve your mixes and recordings (mostly to put themselves out of work: a well recorded track needs next to no mastering).
A good mastering engineer will also have a very good room.
So, my suggestion is to book a session with a mastering engineer, bring your files and have them listen to them and give you feedback. Then, if they think they are good, do some work on them. By getting inside a session, the lessons learned will be extremely valuable in moving forward in creating your music.
Not sure what that has to do with a B3, but I hate moving those things too!