1. Vaya'amein ha'aim vayishmi'u ki pakad Hashem es Bnei Yisrael... (4:31)
Shouldn't the pasuk first tell us "vayishmi'u," that the people heard Moshe's message, and then "vaya'amein ha'am," that they believed it and took it to heart? Ksav Sofer reminds us that the term "am" usually refers to the regular folks, the hoi polloi. The "am" did not think of themselves as worthy of geulah, but the "am" did believe when they heard that Hashem would redeem "Bnei Yisrael," the more worthy members of the people, the spiritual elite. The best they could hope for is to be shlepped along in the process.
I am sure your knee-jerk reaction to the question was to think of "na'aseh v'nishma," the classic example of hearing/understanding take a back seat. The Sefas Emes teaches that Bnei Yisrael had no "na'aseh" yet -- there was not much in the way of Torah and mitzvos that they could do -- but the potential for "na'aseh" was there in the "vaya'amein," the expression of emunah. (Of course, you can flip the relationship the other way as well -- "na'aseh," action, is significant because it demonstrates the commitment of emunah [it's a siman, not a sibah]).
R' Leibel Eiger goes a step further (5631 second seudah) and adds that it is emunah which leads to "vayishmi'u," to understanding and acceptance; in other words, emunah did not simply precede understanding sequentially, it precedes it logically as well. The facts only fall into place for someone who is willing to take the first step of belief in their direction. (This is of course an affront to the modern thinking that forces belief to take a back seat to whatever facts have already revealed themselves as true, v'ain kan makom l'ha'arich.)
2. VaTirena hamiyaldos es haElokim v'lo asu ka'asher dibeir aleihem melech Mitzrayim
Rav Gifter has a beautiful diyuk here. A normal person might have refused to obey Pharoah out of compassion and sympathy for the newborn. Yet, as we have seen throughout history, emotional considerations are a wobbly foundation upon which to build a structure of ethics, as emotions can be swayed and twisted. The miyaldos did not act (only) out of compassion, but rather because of yiras Elokim -- not yiras shamayim, not yiras Hashem, but particularly yiras Elokim = midas hadin, justice. The miyaldos did not kill because it was unjust to do so, not because it pulled on their heartstringso.
Why was the reward given to the miyaldos for not tossing the baby boys into the Nile batei kehunah, leviya, and malchus (Rashi 1:21)? I saw R' Berel Soloveitchik quoted as explaining that although the din is that in a case of an eved v'aku"m who has relations with a bas Yisrael the child is kasher (there is no psul l'kahal), the child would not be accepted for kehunah or malchus where verifiable lineage/yichus through the father's side is needed (though see Tos Sotah 41b). Preserving the baby boys ensured the continuity of halachic yichus.