Advice on interior drain tile

[Kyle B.]

I am going to be making an offer on a home and wanted to get some thoughts on whether or not I should budget to have an interior drain tile/sump pump installed. The home is a 1950's ranch with cinder block foundation, which is very common for the area. From what I could tell, the foundation appeared to be in good condition (ie, no bowing, no cracks). About 40% of the basement is finished and throughout I saw no signs of water seepage. 

If I purchase the home, I would update the area of the basement already finished and keep the remaining portion unfinished. What has other people's experiences been with these types of homes? Do you typically add drain tiles/sump pumps on an as needed basis and just make sure grading is going away from home, or is it more of a must have when a portion of the basement is finished?

Thanks,
Kyle