Character Level boost effects your character's progression in the MSQ, as in you will effectively have passed all the direct MSQ steps to get to level X.
Character Job boost effects the job you buy the boost for, to boost it to level X, however if you haven't progressed your character to at least that level or higher, you can't job boost.
MSQ boost effectively skips the MSQ content for your character, assuming your character is high enough level.

So, yes, boosting effects your character as a whole in regards to the MSQ, even if you decide to try other jobs.

Remember, unlike most all other MMO games, your character is capable of obtaining every job in the game and leveling them to max level, so your character is your job(s) in FF14. Were as other games, your job is your character, as far as leveling and progressing and that you can't easily change.
FF14 - Be all that You can Be!