This sounds like it's more a tone issue than a balance issue, and that's something really only you can address.

If you want a very gritty game with many drawn out, test of endurance, combats then you might have to ask your players not to pursue certain combat options (of which metamagic reducers are simply one of many) which can trivialize encounters.

Regarding what other feats I'd consider aside from metamagics and cost reducers, I'd pick up a good mixture of things which allow me to both avoid combats and function efficiently in non-combat scenes. If you as a player build a reputation for indiscriminately throwing around heavily metamagicked spells, expect the DM to begin having intelligent NPCs invest resources preparing for that tactic. Without contingent spells and the higher order of magical defensives available you might never get the chance to cast all your quickened spells if you fail the wrong spot check.