Hi tractor man,
Well it depends, is the short answer. The Bport will do most jobs the Raglan and tom senior will do, unless they are rare extraordinarily large-model mills.
Taiwanese Bport clones are almost as good and just as durable as genuine Bport mills in my experience, and cost far less, especially used.
For drilling, the common Bports have only 5" quill travel, and the knee can not be easily swung out of the way to drill a tall workpiece (like a tractor half shaft for a hub stud to be drilled out.) If your pillar drill is a floor model that does allow tall work to be drilled, and or has more quill travel, keep it.
The shaper will make a nicer job than an endmill in a Bport on large flat surfaces. Shapers are also really good at deep internal splines, square sockets and keyways too (again common stuff on tractors) and Bports aren't. I would say keep the shaper if you have room in addition to the Bport. For dovetail gibs, shapers can do them with simple single point tools. In a mill, more expensive angled cutters or saws must be used for dovetail gibs usually, unless small endmills are used with large relief cuts (if you ever foresee yourself doing any dovetail gibs).
You will find a Bport ideal for precision drilling and light milling of complex shapes, especially with a DRO fitted to at least the X and Y axes. Bports and B port clones are great for model making in general.
If you buy a Bport used be aware that table gib wear is usually much worse in the middle range of table travel and so many sellers crank the gibs down to make them appear tighter in the middle, but this causes stiffness at the ends of travel. If you are looking at a mill and you can hardly move the table screw handles at ends of travel, but they work smooth in the middle, the mill probably has been "fine adjusted" that way. Transmission and motor repairs are usually relatively expensive and complicated in Bports and Bport clones compared to say a shaper or drill press.
Just some food for thought, and my $0.02, your mileage may vary. Good luck.
JD