I do my own build and I update every week, git pull, ./scripts/feeds update -a / install etc ... and then make menuconfig and save, I hardly ever change my .config , is this ok or with all the updates and additions i should do something else in menuconfig?
I highly recommend using ./scripts/env to save your settings (will also include your configuration). To back up, use ./scripts/diffconfig.sh to save only your local modifications to .config. You can easily restore from there.
You should probably do "make defconfig" or "make menuconfig" always before a build to straighten up any possible package dependency changes or new config items.
Like borromini says, it is more important to keep your changes to .config than the whole .config. using the previous diffconfig output as the new .config may enable you to drop old/accidental dependencies later.