How to get more quests from Vex after bypassing a bug with Heimskr’s house

I don't think that there is any additional information in the quest journal about Miscellaneous quests (that is, specifically the quests that get filled under the "Miscellaneous" category in the journal). The one line in the journal is all you get.

(Which, yes, is a surprising choice on Bethesda's part. Most RPGs will give you a paragraph or two about any quest in the journal, but Skyrim seemingly doesn't for Miscellaneous quests.)

However, if you've forgotten the context of the quest (which, as you point out, is very easy to do), you can always turn on quest tracking for that individual quest. Make sure that quest tracking is turned on for the Miscellaneous category as a whole (in the left column), and then turn on quest tracking for the individual quest in the right-hand list. (And maybe turn off quest tracking for other quests.)

Also, don't forget that you can select a Miscellaneous quest and get a map location for that quest.

These will let you at least find the person, place, or thing for that quest, even if you can't recall why or what you need to do with them. In almost all cases, what you need to do becomes clear when you get to the person, place, or thing.

According to UESP wiki (and my boyfriend had the same problem with his), if for some reason you accidentally exit out of the conversation with Mirabelle before you talk about the Staff of Magnus, you will be unable to ever have that option again. However, there was supposedly an "unofficial patch" that fixed this.

I'm not sure if these circumstances were the same as yours, but, nevertheless, here's the link and I hope it helps!:

http://www.uesp.net/wiki/Skyrim:Revealing_the_Unseen