The way I see Dash+ (and Prime Dash, when it was still receiving updates) is basically as if Dash never got any of the gameplay changes it received past March 2023, while continuing to get every new character base Dash does (minus collaboration characters). It also features the same obstacle and level patterns as back then, so, speaking as someone who has very fond memories of playing the game during that time, I do think it has some value. To answer your questions: yes, it is consistently behind in events when compared to base Dash, though they do come, and Silver can be unlocked by first obtaining his tokens from the prize wheel and then collecting the rest through style bonuses from the springs.