Does your balustrade system look something like this?
New home builders in the GTA and surrounding area's have been installing balustrade systems (Handrails, posts, spindles) similar to this for about 100 years. Yes ... They may have stood the test of time, but their time has certainly come.
It's not just the colonial profile of the Newel Posts and Balusters that dates this staircase, it's the colour! The longer a staircase sits with a traditional coating of an oil based varnish or polyurethane, the darker the yellow/orange tinge becomes. Better to use a water based finish instead.
And BTW, If you plan on sanding and refinishing these Newel Posts, you had better put some elbow grease into it, because if you don't get all of the varnish off, the new stain won't take. You will notices streaks, globs etc....
So, if indeed your balustrade system does in fact look similar to this, then unless you are in love with the colour and style, you would be far better served swapping them out for a more contemporary modern design.
Renovating a staircase is most likely a one event for most people. So if you choose to embark on the project, think it out properly, because at the end of the day what's the point of having beautiful new hardwood stair treads and new iron or white balusters, and then re-install an old Newel Post. Of course the choice is yours, but in our experience, our clients are extremely glad that they opted for new.