Well to answer this part of your post. I guess it depends on each person specifically and what they find worth knowing about. For me though personally; I would say I would only like a thread about an UDFA signing if it was a truly exceptional UDFA which has a realistic chance to crack the 53.
The reason I don't think a guy like Derrick Johnson deserves his own thread is because he is very unlikely to ever contribute here. Dobson, Edelman, Amendola and LaFell are almost certainly staying. Also with Slater on the team there is likely only 1 spot left.
Thompkins, Boyce. Harrison, Gallon are all competing for that spot and likely have the inside track over any UDFAs. I just don't see a guy like Derrick likely to ever make an impact on this team. But you never know. He could be a Victor Cruz for all I know.