I sometimes do this but I've learned to avoid things I liked a long time ago as watching them now can ruin them for me. I guess I'm much more of a critical thinker now so, instead of enjoying a show, I might notice nuances that I hadn't noticed in my youth and it can be quite disappointing. The first thing that comes to mind here is the old G.I. Joe cartoons. As a kid I just took them as being about a superhero. I obviously didn't realize that the cartoons were basically propaganda films. On the other hand, I think I've seen most episodes of Lost at least twice.
I think it depends on the individual series. For me, I was a child in the 90s, so the programs I watched were cartoons. There are timeless cartoons that adults love just as much as kids, but then there are kids shows that are just for kids. I have fond memories of many kids' shows, but if I were to watch many of them today, I would be disappointed because I have grown out of them. Best leave those ones as a memory.
Of course - how can you avoid it if you have Foxtel. But I can't watch just any or all of them - and no 80's shows at all not even Cheers, unless its the ones with Kirstie Alley - Shelley Long annoys me so much!