Yes, on both counts!
Ear pads are actually one of the most critical aspects of headphone tuning, and any time you change the default pads you’ll notice changes in sound signature. Usually, velour ear pads will have less bass response and a slightly more open feel than leatherette pads, because they don’t keep as much air from escaping.
Over the years, numerous companies have tried to mitigate these “problems” by combining different materials. Some velour ear pads will have a leatherette outer or inner wall. The Arctis series from Steelseries uses a leatherette layer underneath their sports fabric. Brainwavz sells “Hybrid” versions of the HM5 ear pads that use this technique as well.
The soundstage gains of velour aren’t massive, it’s just a slight bit more openness…but you’re losing bass response and isolation in the process. So it’s all going to be a matter of personal taste, and you won’t know if you like it better until you try it.