I totally agree. For some reason, I find when doing Rehraas Sahib I actually open my mouth a lot more (sounds weird), i.e. I really try to get the pronounciation of every 'tipee', 'adhik', etc., properly spot-on. It also seems to just flow so beautifully that you can't help but become almost lyrical when reciting Rehraas Sahib Ji.
Yes, your point about having more time during the evening is very pertinent, as well as some days one REALLY tries to thoroughly comprehend the meaning of Gurbani by dwelling on each Gurmukhi word that little bit longer.
When I first started doing paath, I knew there were a couple of pronounciations I wasn't doing correctly - they just didn't sound right to my ears. So I got a CD of Professor Satnam Singh and listened to his pronounciations, and thankfully I've began to improve quite quickly. Luckily I don't have that quirk of some Western youngsters who try to speak Panjabi / Gurmukhi and the harsh sounds of a word are softened into weird, amusing sounds. For example, a car is pronounced "gaddi" but sometimes the youngsters say "gadhi". :D