Not many agents like to answer $/SF questions, do they! That's understandable, since SF numbers around the District, (from tax records in particular), are notoriously inaccurate, and through law-suits, agents have been reticent to state them themselves. That's a shame, of course, since its usually the second question a buyer asks me about a house or condo!
Nonethelss, $/SF averages can be calculated, and are a quite useful means of making comparisons. This must ALWAYS be done between apples and apples, however, so a neighborhood average is a tough-call. It is easiest within a single condo building, (for obvious reasons), and then between very similar properties where full information about each is accurately available.
I use this measure as a 'first cut' at the time when I'm building an offer for a specific property. It's also part of what professional appraisers do in their work for lenders.
With respect to your question on Foxhall Village, Burleith and the Cloisters, I'd venture that figures on the Cloister town houses can be calculated quite easily, (because they're all of similar construction, built at the same time!), but a bit trickier for FVillage, and least practical for Burleith, where there is a wider variety of houses, (apples, oranges, peaches, a few watermelons~!)
Prices have been steady-to-up in the District all year! Where are they going? If I could answer that...