I don't know about you, but the game looses some of its fun for me when the main skills for my current build hit 100. The idea of topping out and not improving at all is a bit of a drag so I tend to legenderize the skills that hit 100 and keep things interesting.
However, it's less daunting to play without certain skills than others. For example, I'll roll over Smithing and Sneak without much of a second thought. They both rebuild relatively easily. If I perked Speech or Lockpicking, I'd roll those over too.
Some skills seem worth the risk - maybe the armor, block, and melee weapon skills? Archery, however, doesn't seem worth rebuilding given how long it takes to reach 100 (especially if you don't train).
However, essential mage skills (Alteration and Illusion in particular) seem like suicide to roll over. I don't think I've ever tried those. Maybe Destruction would be ok?
How do you players strategize this?