zonomo:
Some folks divide all tobaccos between "aromatics" and "English" blends, just as an easy generalization. Technically, though, an "English" consists primarily of Virginias, orientals, and latakia. Latakia seems to be one of the defining tobaccos of a true English blend. (Such definitions aren't set in stone, however.)
Your HH Mature Virginia is something of an oddity, in my opinion. To me, if you call something "Mature Virginia," then it should be exactly that: a matured Virginia blend. According to the information at TobaccoReviews.com, though, this blend actually has 22 different tobaccos in it! It also includes burley, orientals, and cavendish. So, again in my opinion, it will taste nothing like a matured Virginia that is made solely of matured Virginias. For example, it might be interesting to compare this blend with others, such as Butera's Royal Vintage: Matured Ribbon. I think you'll notice a distinct difference. (I should also confess that I'm not a big MacBaren fan. I have no idea how they got to be so popular.)
As Chris mentions, pipe dedication is up to you. I do it -- I have at least seven pipes for every different category of tobacco I smoke (and that includes straight Virginias, Virginia/burley flakes, English blends, Balkan blends, aromatics -- which I only smoke rarely -- and Penzance, the only individual blend for which I have dedicated pipes). I do think I notice a difference by doing this; it seems easier to get the most from each particular type of blend. That said, I went for several years with just three or four pipes, smoked everything in all of them, and enjoyed them. If that's your choice, just keep in mind that it typically takes at least three bowls of a blend before the previous blend disappears and you can really taste what you're currently smoking. (And there are a few blends that are notorious for permanently "ghosting" a pipe with their flavor.)
Bob