Did you know that you can just leave Peak 15 without purging the Hot Labs?
I was actually the other way round. It took me about 3 playthroughs to realize that you can even go into the hotlabs. Now I always do the whole package, first the quest to get the key for the maintnance tunnel, then the hotlabs, then back out and getting ambushed by Cpt. Riley Ventralis, then Benezia. Rift Station is usually a graveyard when I leave it. 
BTW, I rode a lot of elevators on the Citadel yesterday before presenting Tali's evidence to the council. On about my tenth ride, I heard a news message about how Udina tried to get Saren dismissed from the spectres and failed. Looks like you can only hear this news message before you get a spectre. I am not sure but I don't think I ever heard this message before, probably used too much quick travel in previous playthroughs.