I didn't know of this usage of ours and yours, so to try and get some data I sifted through lists of hists in two corpora: the British National Corpus and the Corpus of Contemporary American English. I looked for “at ours”, “at yours”, “to ours”, and “to yours”. I went through the hits to check for context in each case. What I see is:
- There are a few results in the British corpus matching your described usage. All of them come from spoken sources (conversations recorded and transcribed), with no such hit from written sources (magazines, fiction or whatever). I would hazard a guess: maybe these few hits are all from a given geographical area or dialect, though I could not confirm it (could not find any detail on the sources in the BNC search interface).
- There is no such usage recorded in the American corpus, which would tend to indicate that it's indeed a regional usage.
That conclusion is not definitive, however, given the relatively low number (a dozen) of matching records in the BNC in the first place. (Absence of evidence not being evidence of absence, unless you have great statistics.) However, that's the best I can do.