Lapping them will tell you if everything is correct or not with the seats and valve face. I always lap them but you do not need to blue them and this can actually inerfere with the lapping process.
Also, not all cylinder head machinists do the same level of quality, therefore, it is entirely possible that if you have them redone, they might not be as good as the are now, and if this occurs, you would have paid to have a lesser quality job done on them.