I think that flamebringer is right. Aero-eng is a totally different field to maintenance engineering, and these top-ups are of little value as a design office would quite rightly regard you as a maintainer who has no real academic background, nor enough maintenance experience for them to be able to use.
You'd be better off looking to something like a management degree if you want to progress your career in the coming years.
If you want to switch to design, at the stage you're at, you'd be better off building up some years of real maintenance experience, get a maths qualification, then look to a structured way into an MSc.
Either way, real on-the-job experience is what you really need, not additional bits of paper.
I'm doing some work with Emirates College at the moment - they look to be good chaps and well resourced, but the same still applies.
G