Yeah; I have the same reaction when I visit my best friend at her 7,000 square foot home that she shares with her husband (no kids or pets). They have a pool and tennis court. They bought it about the same time that DH and I bought our much more modest (but still really nice to us) home. She lives in an affluent suburb while the town I live, well, not affluent. It's a bit of culture shock.

As for a housewarming gift, I'd go with a bottle of wine and something homemade, like cookies,....or nothing. Honestly, I only got a handful of housewarming gifts when I bought my first house. With my second (the one I got with DH just before we married), I got nothing. I'm not entirely sure they're the norm anymore.