I guess the question is can you really obtain a professional quality recording with NT1as?
Yes, absolutely. I recorded my debut CD using one. Its a perfectly good mic and very quiet.
BUT, that's not the only issue and everything else in the chain affects how close you can get to a pro quality recording:
-your guitar (until you actually start recording your guitar you have no idea how well it will record).
-your playing skills
-the preamp/audio interface (I don't have any experience with the Mbox but the preamp is crucial)
-the room (you can't underestimate this one, it can be a real pain to solve)
-your recording skills (miking up etc)
-your production skills
When you hear an amateurish recording it can be down to one, or more likely a combination of these factors.
The Rode is the least of your problems
rather than spend a fortune on a Neumann you need to practice recording and get to grips with all the above, it takes time to learn and troubleshoot and throwing money at an expensive mic does not catapult your quality up, you may end up (as one of my friends discovered) actually making a problem that's already there worse due to its sensitivity.