Yea, don't forget headwork too, MWR valves don't just "slide right in"
Nothing wrong with stock 2ZZ valves, the springs and retainers are what you should be concerned with. The main reasons 2zz valves get bent are mishifting/overrev and valve float. The first thing can be corrected by the driver, and the later problem can be corrected with stiffer valve springs.
Factory valves are the best comprimise between strenght and weight. MWR valves will flow more, but the head must be machined to accept them.