Don't those visor designs on GoGo-V's helmets look kinda random? Actually, no; the shapes are designed after - or rather, taken directly from - the crests of the respective rescue divisions each sibling worked in before quitting for full-time activity at Super Rescue Labs. Sure enough, they still pretty much take the same roles as GoGo-V.
Y'know those giant explosions that always accompany a giant monster/robot battle? The Max Victory Robo is built to use them. Think about it. If there's ever a colossal fire anywhere, all GoGoFive needs to do to save thousands of lives is take a walk in the Max Victory Robo.
Why is the series called GoGo-V? Well when you realise that Go is japanese for five, you see that it is Rescue Sentai Five Five Five: Japan's emergency number
An obvious one is this: Why is there no Sixth Ranger? Because it would ruin the title.