I've heard that valiance is a great sidearm, but would I use it with my current arsenal?
SWORDS
Combuster
Gran Faust
Final Florish
GUNS
Storm Driver
Sentenza
Blitz needle
BOMBS
none
ARMOR
Vog set
Shadowsun Set
SHIELDS
Barbarous Thorn Shield
Swiftsrike Buckler
As far as sidearm guns go, Storm Driver does better damage and status. But Valiance does a fair amount of knockback, and you don't have any knockback guns, so you could give it a try maybe.
If you're bored with the game and don't know what else to do, then get Valiance. If you have any other pressing equipment needs (such as ANY BOMB) then get those first.
You dont really need it. But that doesnt necesarily means you wont enjoy it. I'd rather increase my armor/trinkets options tho.