There are measurable fundamentals that consistently lead to local real estate appreciation, like population growth, economic growth, increasing mean income level, school district ranking, nearby commercial development, nearby infrastructure development, etc.

Of course all of this can be trumped over short time periods by nationwide trends like the recent financial crisis. But with strong local fundamentals, such trends create more volatility than permanent depreciation.

> I get that building a pool makes your house worth more

Not necessarily. Many folks see a pool as an extra expense and will immediately disregard a potential purchase because the property has a pool. This is especially true for above-ground ones that aren't as durable as in-ground designs.