One question I didn't want to answer when my application was under deliberation was: YES, did the Vegemite make the MOINK balls taste better than those without Vegemite.
Yes they were better, but only by a bit, because I really didn't want to overdo it. I paid strict attention to trying to keep the mince and seasoning as simple and plebian as possible. Vegemite is a yeast extract. Its origan was as a by product of beer fermentation Vegemite itself has a very intense flavour and this can be extremely offputting to people not familiar with it... who may treat it like any other spread and slap it on thick like honey or peanut spead and then get a big surprise.
Basically, you just start with a little bit and see how you like it. As an additive to foods, you'll see yeast extracts in all sorts of things and they are mainly flavour enhancers. So, like when you whack some Worcestershire Saue, or Balsamic Vinegar into a hearty stew for that flavour boost, you can also do the same with a bit of vegemite... Now, I would not necesarily recommend whisking a pound of the stuff into the next beef bourginourne you make...(sic)... I DO recommend adding it to abasic meat pie mix or home-made burgers for that little bit of a zing... A tablespoon a pound would probably do the trick...
Give it a whirl!