I gotta say I love the cute mecha look of the spiral knights... and so I would like cute mecha tanks and heavy armaments. Cute little spiral tanks themed up like their helmets charging down their enemies, blowing down walls, all the fun stuff. Vulcan cannons and rocket launchers to fight enemy hordes. And enemy castles to tear down to make best use of the weapons.
I'd see this most easily as a PvP thing, castle vs. castle, blow down towers and heavy doors and destructible walls like a siege. I can see layers of the clockwork being enemy fortresses that you could go through normally if it'd be very hard to assault or grabbing a missile pack and plowing down enemy barracks. Be a good excuse to pull out bigger enemies of non boss varieties and enemy vehicles, maybe even little air battles with spiral blimps and mini-missions in the layers.
Obviously that would be a ton of work then there's the question if they're be a garage to have a personal vehicle or pre-mades available where needed but I'd fully endorse the Spiral Heavy Arms Corp.
In Spiral Knights, you are meant to be knights, not tank drivers or pilots or the like. It is bad enough them having guns and bombs. Having more and more non-knighty stuff just ruins the knight theme.