It's so personal really! Some people like to rescrap the layouts to reflect their current style. Keep in mind though that your style will likely to continue to change and evolve as time passes so layouts you do now will probably look outdated in the future. Some people choose to keep the old layouts because they show where they were as a scrapper at that point in time and still serve to tell the story of the photos.
Looking back at my old layouts, I have mixed feelings. I started digiscrapping in 2004. To put it quite simply, scrap kits were not then what they are now. Every element was very digital looking, scanned elements were almost non-existent at the time. Most papers had the same canned photoshop textures as well. We had a lot to learn about shadowing back then too. I look back at my layouts and I remember how amazing I thought they were at the time though and that makes me happy, but I still don't like them compared to my layouts now. Some of them I have, or will, rescrap. Others will be left as is. Those layouts that I am redoing are mostly ones where there was more story left to be told. Perhaps I didn't journal as much or left something important out. Perhaps the layout just didn't convey what I was going for and now I have a better idea of how to make it feel the way I want it to. Those are the ones that will be done again.