[SamReidHughes]

Speculative property price increases won't cause an increase to rent, that's a function of what prices the market will pay for housing at particular levels of quality. It might cause somebody who'd buy a home to decide to rent instead, but remember that somebody else is currently occupying that home (or better yet, renting it out). In areas with room for development, speculative price increases on housing will make it profitable to build more housing, which will lower rents (i.e. make them rise less quickly).

Note that property price increases are often associated with increases in rent, but they don't cause the increases -- rent increases is caused by influxes of population, decreases in the population's price sensitivity, etc. Property price increases are caused by the same thing, and speculative property price increases are caused by (among other things) expectations of that sort of thing.

The big difference between houses and milk is that houses are durable goods which don't completely depreciate.