if .cc and .tv are available now, they may not add value later.
now if they were currently owned by someone else and had viable websites on them...and you had the .com, then it's a different story.
other exceptions are, if the other tlds/cctlds/gtlds etc. get traffic or you plan on branding the domain.
though many LLL/NNN collectors probably would like to have same in .com/ .net/.org, but i doubt they'd go far down the line after that.
as is, having .com alone can get you what you want, if the right buyer comes along
there are a few domains were i have same in other extensions, because i figured they had traffic/revenue too.