Still+ silent spell is cool, thematically. But it's not good in NWN, at all. In fact, it's not usable in NWN at all, unless you take autostill or autosilent.
I think we should reward cool thematic options more.
Presenting: the "Stealth" metamagic.
Granted automatically to those that have both still and silent spell, the "Stealth" metamagic combined their effects with an accompanying +2 spell level.
For bonus points, please remove casting animations from stilled spells, using the feat, autostill, or this new metamagic.