Personally, everyone playing a Gunner should at least invest a point into Chain Trigger. It's not costing a whole lot to pick up since it's the second tier with the same unlock cost as Zero Range Advance, and it has some uses. Chain Finish, on the other hand, I'm rather skeptical.

Showtime, on the other hand, I'm very strongly considering picking up, for the sole reason of becoming a dodge tank. Think about it, we have all these invincibility frames and dodges from TMG skills, and with Showtime upping hate and Gear Gauge, we can potentially dish out some good damage along with nice hate generation. So I'm working my way towards that unless something comes along to talk me out, but that seems unlikely.