If you can swing it, I'd add a good quality black or charcoal spring weight wool suit to your collection, several good-fitting cotton white shirts (avoid blends if you can), some snug white cotton tees, and a small collection of smart ties. DC tends to get pretty humid in the summer, so the shirts will help you stay cool and sharp. White sets off any tie without having to think about whether it "works," so you can get dressed quickly and still mix it up with a variety of ties. Ties can be expensive, but there's always one or two good ones on the sale racks.

As for shoes, I would avoid buckles and stick strictly to lace-ups, avoid any trendy toe shape, going for a substantial leather-soled oxford that you can keep polished to a high sheen. For a long-lasting shoe, I'd budget $80-120. See Johnson & Murphy, maybe.

Yes, you'll look like a consultant, but this is a look that says you mean business. It's a good interview look, too.

Good luck, and post pictures!

Rex.