We're looking at the difference between great and very good, looking at Wilfork's career ups and downs. I think he will play very well in 2015, somewhere - possibly (even now) in NE. I think he will decline to good. He will decline to JAG, if still playing, at some point, but it is not known when.
I disagree that his increasing age will necessarily equate to increasing weight.
I think it will be very difficult to keep VW (but it does depend on his desire to play for the Pats, as we all dream, on the cheap, relatively speaking.)
Similarly it will be very difficult to replace VW. We will be in terra incognita, and we will deal with that. We will make best use of the DTs we have on the field. If we don't add one in FA, and Vince walks, it will be a weakness going into '15. Expecting a rookie bonanza is a pretty risky road, on a first-year basis. We'll simply be swapping out our former secondary problems for problems at the D-Line.
My best guess is an affordable FA replacement. I do not think a 1st round pick at DT is inevitable. While it is true that "tie goes to the position of need" in NE's drafts, I think they're predicated on value. So if 4 DTs go in the first-round and there is a big drop-off (as the Pats evaluate, not some draft guru) between their 4th favorite and 5th favorite, and for some reason a ****-hot corner (by their evaluation) is on the board, I think they pick the CB.
Once again this is a pronounced tendency over time. Of course need is also present in Patriot drafts but I think that more than other teams, the card stacks are merged into one "value" stack, to use an anachronistic metaphor.