I agree with the comment "quality over quantity". Here would be my five choices, given your situation: 1. black captoe oxfords (a very conservative business shoe, it can be worn with a suit, with business casual, and is also acceptable, though marginally so, with a tux. The AE Park Avenue is an example, though I'm not fond of AE shoes and every shoemaker will have a black captoe oxford in the catalog). 2. dark brown punched captoe oxfords (Also suit-appropriate, but more interesting than a plain captoe. It can be worn with business casual. Again, every shoemaker will offer one). 3. brown or burgundy double-monks (Brown shoes can be worn with any shade of trousers except black; burgundy may, in principle, be worn with any color trousers including black. My favorites are the JL Chapel, pictured here: http://www.leathersoulhawaii.com/200...n-museum-calf/
though not necessarily in the color shown) 4. A brown boot with rubber sole for rain/snow/slush. I like the CJ Tetbury chukka boots because they're shape makes them slightly fashion forward (can be worn with business casual and casual, including jeans). http://www.pediwear.co.uk/crockett/products/1432.php
5. Your walnut AEs. If you have the money to buy a fifth pair and really like double monks, get a second pair, perhaps in brown suede. These shoes would work with business casual and casual, including jeans (depending on their styling. For example, I wouldn't wear JL Chapels with jeans).