When I started collecting, I was told to buy the best you can afford.
This hobby does cost a lot of money if you are going to buy the best all the time, that being said, the only time I would buy a net graded note is if there are less than 10 population. When being so few notes available you are not left with to many options, an example of this for BOC would be a 1954 E/R test note as there are few known to this day.
You did get it right though, as you have to make a decision on price you would pay for a net graded note. Eye appeal, missing pieces, repairs, tears all are reasons to lower the amount you would be willing to pay for a note. If you don't get it there will usually be another one come up. If you are unsure whether the note you are going after is rare or common, research the internet for that series note through auction sites and see what has been active with them.