Airmanship is always a good idea. However only using half the gust factor is nowhere suggested in the boeing manuals. With the last revision we even got new wind limits which explicitly include the whole tower reported gust value for all wind limit calculation including crosswind.
Anyway, trusting the automatics is not completely bad, but especially in gusty conditions it is a very good idea to disconnect both autopilot and autothrust (remember: boeing recommends manual thrust in manual flight) and just fly it manually. A 30kt crosswind is out of limits by 5 kts for autoland anyway so you have to fly it manually at some point anyway. Additionally is the NG autothrust pretty slow and not the best thing to use in bad conditions.