Half dimensions

If datum feature B were the left side of the shown plate (or the right side for that matter) AND 14 baisc dimension is added between the datum feature B and the closest hole, THEN do we need 30 baisc or not?

In other words, as shown with datum B, being the centerplane of the part, 30 basic is not needed. Agreed with that.
What about in my modified scenario? (again, datum feature B moved to the side and 14 basic added). Do I need 30 basic or is considered implied? (30 basic is the dimension from the center holes)

Here is a sketch:


If you have a copy of ASME Y14.5M-1994 then you can see on page 84, figure 5-3 and 5-4 the recommendations for dimensioning a set of holes almost exactly like your example.

Above is a snippet.