The stat value of the jewelcrafter-only gems doesn't change, So if you are only interested in the gems, No need to level past the point where you would learn/be able to cut them.
Leveling past that point, up to 450 let's you cut Wotlk-grade epic gems, 20 agility, 20 resilience, 25 spell penetration, Etc. Quite a few people still buy/sell said gems, as this is a decently-sized bracket, Find a cheap 20-50g uncut on the Auction house, cut it, sell it for 120-250, depending on your economy.
But yeah, whatever works for you.