I read a little about this subject recently because I’ve used a few public domain PSAs and commercials as short, illustrative clips and I’ve a project on the back burner that could make extensive use of them. Cleaning them up to a uniform quality would be ideal.
For improvements to reasonable quality sources, colour adjustments etc. SC should be fine, but for more detailed work or badly damaged sources that need frame by frame spot work, or complex algorithms for stabilising or denoising and cleaning, I’ll be using a specialised tool. The two packages I’ve linked below are free or open source and appear to be up to the task (for my needs at least). I’ve downloaded but not used them myself yet so I can’t vouch for them personally, but plenty of their users do.
http://videocleaner.com/start.html
Videocleaner was designed for enhancing video/images for use in criminal evidence but potentially has far more applications in it’s reach.
http://contact41766.wixsite.com/film9/blank-1
Film9 is specifically intended for restoring old film and the demo video demonstrates some impressive results.
You may also want to look at compositing packages like Natron which provide many tools that may fit the bill for your needs and offer some amazing possibilities for other tasks.