I'm a huge Jessica fan but I would say the b-sides of Lion Heart & Holiday Night are fantastic. Yes I think the sound overall did suffer but there are still some excellent OT8 songs. Also I like that other members got more of the spotlight, it was great to see Sunny, Yuri etc get great lines and coverage along with TTS.
I'll always prefer OT9 but I wouldn't say SNSD got sub par afterwards, but I guess it all comes down to personal taste. All the members are thriving and doing really well in their respective solo careers so that says it all really - I can't really think if other inactive groups that have this.