I just did one, but I didn't go too far with it. I just removed the terrible titles that were on it and made a slick little intro set to "their song". The original had some of the most awful jazz track music with bright yellow cheesy fonted titles that were not even symetrically aligned. The main thing for them was getting it transfered to DVD, so just having a nicely printed DVD (the photo they wanted to use had the top of the grooms head chopped off due to poor framing from the photog....I photoshoped the rest of his head in and it looked amazingly good) and custom DVD case with selection menus meant a lot to them.
If youre not already overwhelmed with work and could use some little things to supplent your income, I think it's a pretty viable service. There are tons of people with little crappy VHS weddings that would LOVE to have such simple little upgrades without completely redoing it. And though the video quality was already fairly poor, I noticed no significant degradation. She checked it out before leaving and was thrilled beyond description, so I wouldn't even worry about that.