First, my apologies. In reading my post again, I see that it could be taken as an attack on your post and/or you. That was not my intent. My intent was to note the folly of a surprising number of people who are out there with the "good, get rid of Welker" stuff. Now, onward...
It's no guarantee, but let's be honest here. This was the youngest (I believe) defense in the NFL last year. There should be real improvement there, regardless of what moves are made.
Jones/Ninkovich/Spikes/McCourty/Dennard/Hightower are all players who should be improving at the positions they play, from experience alone (Ninkovich's role change is why he's on the list).
Moving on from Welker doesn't mean that they improve the defense. When you look at the cap space, there is basically enough room to sign 2 of the 3 "big free agents" if they don't use the tag on either and they backload the deals. After that, the money's gone. So, whether it's keeping Welker and Talib, or it's letting one/both of them go and having to find replacements, there's not going to be a lot of cash for big name layouts, absent some cap shenanigans.
Basically, letting Welker walk probably accomplishes almost nothing positive, because replacement issues are going to be a huge question mark that the team will either have to overspend to deal with or decide to approach next season with hope and prayer as their only real options.
Yes, but this is one area where they've screwed the pooch with some regularity, and that's the concern for me. It's (almost) never who you cut loose that's the problem. Replacements are usually the problem, and this team has had its fair share of issues there when they've had to replace the top players on the fly.