OK, I don't know much about the Roman period at all, but I do have some thoughts.
Firstly, I don't know what precise problems were caused by the debased coinage, or how the situation came about, but I would say that 'money' as a medium of exchange needs to be easily recognized, easily divisible, portable, hard to duplicate, and it must be a good storer of value. If the debased coins did that, then it didn't really matter whether they were pure gold or not. Of course you do have to take into account how people thought about the 'value' of the coins. If they thought they were worth less, then they were worth less.
Secondly, usually, in an industrial economy, if you vastly increase the money supply without increasing production then you end up with inflation. Now, the Romans didn't do a lot of industrial production - their economy was primarily agricultural and mercantile. A huge boost to the money supply might be expected to increase inflation...however, I don't think it would have, mostly because most people didn't operate in a 'money economy'.
Thirdly, there have been periods in history where the economy had a restricted money supply (due to the absence of enough gold) - and this hindered economic growth. When gold reserves were discovered, they had a positive effect on the economy. It allowed more goods to be exchanged and more...stuff...to happen and remember, in an economy, it's not the existance of assets that is important, it's the movement of assets that is crucial. Money allows that to happen, and if you have too little of it to go around then you're capping your growth. To be honest, I have no idea if this would have been the case with the Romans. I have no idea if their economy did have a poor money supply or if their needs were met with what gold they had.
Anyway...for someone who's been talking out of his ass...those are my thoughts.