In Tiferes Yehonasan, from Rav Yonasan Eibeshutz, an interesting take on the small aleph in the word Vayikra.
He actually considers it to designate a pegam in Moshe! For Hashem said to Moshe לֶךְ-רֵד--כִּי שִׁחֵת עַמְּךָ, אֲשֶׁר הֶעֱלֵיתָ מֵאֶרֶץ מִצְרָיִם, and we can interpret lech red as a reduction from his greatness. Because of an error of insisting on bringing along the Erev Rav, and converts are as difficult to Israel like a sore. And this was the primary basis of the sin of the Golden Calf. And thus, Hashem's punishment of Moshe, for causing this damage, by removing him from his greatness. And his support for this is that אלף means cow, as in שְׁגַר-אֲלָפֶיךָ וְעַשְׁתְּרֹת צֹאנֶךָ. And a small one means a small cow, which is a reference to the golden calf.
A very creative interpretation. Shadal has another explanation, that the small aleph had no deep meaning, but was an artifact of an old practice to not maintain spaces between words, and to not write letters which would appear in both words, and thus the aleph beginning the next word אל made the one of Vayikra drop. Aside from this, I would suggest that as an em hakriyah, this as well as many other final letters of Ehevi might have dropped, and that is the significance of the small aleph in this particular high-profile world.
In the "famous" interpretation of this phenomenon, the aleph appears to be interpreted in a very different way. The theme of the first pasuk, based on the preceding context (see Baal HaTurim about his glowing face) and based on Hashem's designation and calling out specifically to him, is to give to Moshe gedulah. And when they notice the small aleph and the resulting ויקר as a parallel to Bilaam, this is attributed to Moshe Rabbenu's initiative, that he was a great Anav, who tried -- which in turn is also an attributing of greatness to Moshe. (Or perhaps other midrashim connecting Vayikra to Yoker.)
That is not to say that Rav Yonasan Eibeshutz's interpretation is without it own internal support. ויקר is then not so flattering, and the small aleph can be interpreted that way, as Chet HaEgel. And he is surely not the first to say the Erev Rav were responsible for various troubles in the midbar. Just that this local interpretation it runs contrary to the theme Chazal try to develop in their midrash, of Moshe's greatness, and that it might run contrary to the gedulah inherent in Hashem specifically singling out Moshe for calling in this pasuk.
I admit that on an emotional level, the message in this interpretation bothers me. Even if ultimately it caused all these problems, Moshe as a personality was such that he strove to defend the weak, and so his championing the cause of Datan and Aviram to save them from the mortar was a sign of his greatness, IMHO, even as it ended up causing tremendous problems. (The purpose of that midrash might have been about questioning the middot of Hakadosh Baruch Hu.) And the acceptance of gerim and bringing them under kanfei haShechina, even if ultimately it caused a bunch of problems, should not be judged by later generations in hindsight as something negative. The effect was negative, but the act was reflective of the personality which exuded gedulah, not the opposite.