No, I don't think they should. 1) because people are way too obsessed with Tali as it is and this is a move bound to piss people off if someone's like "RARGH YOU DIDN'T MAKE HER HOT" and 2) because it undermines the whole situation quarians are in. I love Tali and everything, but it kind of annoyed me that she took her helmet off and made out with Shepard if he romanced her. I just thought it diminished the impact of her situation and made it kind of shallow. Just my opinion, though.
Although, there are two situations where I would be totally comfortable with them unmasking the quarians where I think it would be poignant and not out of place at all. Firstly, if Tali dies. Removing her mask and seeing her face if she's fatally wounded would be a really touching moment; she already knows she's dying so she wants her final gesture to Shepard to be the most intimate thing a quarian can do with another - being outside their suit with them. Secondly, I think it would be a really uplifting, triumphant moment if the quarians step onto their homeworld for the first time in centuries...and can finally take their helmets off, even if only for a minute. That would be a great thing to have happen, and I wouldn't object to it at all since it represents the completion of what has been the quarians' dream for centuries, and their freedom. Tali would obviously be among her people then, so we'd get to see her face too.
Other than those exceptions, I don't see any reason why they should take their helmets off and reveal what they look like. Personally, I think anything else would come off as too contrived.