I would still suggest using not only troops, but also units from other games, and not just from the fifth installment. Magic would look great, it would be nice to add castles, but... since there are two races per suit, it might not look very good... artifacts would also look a bit bland, with the exception of the aforementioned blades. And, yes, by the way, maybe we could try using heroes from the fifth game? (portraits)
What about the idea of including creatures from two opposing factions in each suit?
Clubs - Dungeon and Sylvan
Spades - Necropolis and Gnomes
Hearts - Inferno and Haven
Diamonds - Orcs and Mages

But overall, it's turning out quite well ;)