Extra combats and vehicles work well together considering some of the best vehicles have attack triggers, including Smuggler's Copter, Skysovereign, Consul Flagship, and Lumbering Worldwagon
Sure, when you have an overlap on the board and some spare mana Grenzo is a pile of value but in that situations you have probably won anyway
If we can benefit from any spell as long as it can be played on their turn, I want to load up on all of the 75% spells I can to make sure we're pilfering their cards, thus getting us even more value
What is there not to like here
This is also just a classic green creature and an elegant design that shows off greens ability to ramp and fix and shows how life is at the root of all colors
As simple as that, what more do we need to say