Yep. Also in DC, also with limited space (677 sq ft for 2). The space issue does factor in while shopping at Costco. For example, sometimes you can't justify (or at least, can't persuade the wife) the huge jug of cooking oil even though it would save you money over the course of its use but we both agreed we didn't want a jug of oil just sitting on the living room floor. We also hike a fair bit in and around NoVA on the I-95 corridor (Prince William Nat'l Forest, Mason Neck, Leesylvania, etc.) and go to the Costco in Woodbridge for the gasoline as well. Gasoline is typically about 40 cents cheaper than where we live in Alexandria. Filled up for $3.34 (plus the 3% back the Costco Amex, so more like $3.24/gal) on Sunday after an all-day hike at PW Nat'l Forest, a great day!
I can't attest to your natural food preference. You may or may not find it to your standards. Why don't you go with someone to visit and do some serious price-checking and QA before taking the plunge? Keep in mind they do have other things besides food like clothing and a pharmacy to name some categories.
It's kinda fun to do (price-checking, book perusing, appliance browsing, walking a leisurely mile or 2) and my wife seriously looks forward to running from aisle to aisle to try all the samples while I am similarly humored/entertained by the sheer sizes of the packages/containers in there and the sheer thought of processing the logistics for a place like that. Never gets old to me but I will be the first to admit shopping at Costco isn't really life-altering or that much of a financial shortcut given our consumption and cost of membership. When we have kids, the utility of the place will surely go up but for now it's really more of a break-even enterprise with some fun and cheap gas sprinkled in (and the place to go when we want to splurge on buying pistachios). YMMV, especially with less space than we have, if you are a single person household, lack of a car (a great thing for you though overall as spending $0 is better than spending even a discounted amount, just if you do have a car and use it and are frequently in an area where cheaper gasoline is being sold, why wouldn't you purchase it there?) and your food preferences. Definitely scope it out beforehand.