If I do get a rhinoplasty, will my voice become less nasal-sounding?

HiI agree with Dr. Bridges.  Any changes to your voice depend on the changes to the internal cavity and the nose.  There are always some usually temporary voice changes due to the nose becoming congested and sinuses filling up with fluid.  Most of these usually resolve.  However, if your septum was very deviated and your turbinates very enlarged and these get fixed, your voice may change.  If the nose is very large and if it gets quite a bit smaller, the voice can change.  These are independent of any possible voice changes as a result of anesthesia issues with the voice box.  We are just talking about quality of the voice.  Ultimately some people have learned a certain speech pattern and even with a perfectly open and airy nose still talk in a "nasal" fashion.  Speech therapy can help in those cases.  First thing is first, your nose needs to be examined. 

The answer depends on what the inside of your nose looks like and your functional symptoms.  If you have nasal obstruction or sinusitis that is corrected, after surgery sometimes the voice will be less "nasally" because you may have more airflow.  Hope this helps...