The syntax of the assembly language is so simple that using Spirit would be an overkill (I was pondering to go with Haskell/Parsec but didn't, for that exact reason).

Spirit is extremely concise. In what way do you think it's overkill?

I just don't think it's necessary to bring in such powerful libraries for something that can be easily accomplished with simpler tools. After all, it makes your code easier to understand for people who are not familiar with boost.

It is true it adds an external dependency.