Conversions are mostly humbug.
Good game designs are often a marriage of vision, genre, and system. Most conversions are about generic systems trying to get a slice of the Vision (or market) of a cool game. GURPS has done many cool source books and conversions. I'll take the source books and skip the conversions.
Updates to good games are often good updates. They improve or update clarity. Where updates "revamp" something so you have a hard transition, you can lose fanbase, but I'll not comment on business practice and management.
Updates also usually mean someone cares or thinks the System is good for another ten years. That's always a positive sign of finding other players to work with.
Reboots. I haven't experienced any of these, but I have both good and bad things buried in my bias about them. First, a reboot brings a chance for an even better story built on something from the past. Second, a reboot can signal a lack of creativity. When 'management' says, 'start over', its often because they think they are out of ideas or have painted themselves into a corner.
How long before the reboot needs a reboot?