Saturation of durable goods
"Durable goods" are a form of utility-generating capital. But they are capital, and what is actually generating utility is the flow of services from them, not them directly. So when we buy a durable good, this is not consumption, it is investment. The phenomenon of uneven intertemporal allocation of purchasing expenses in durable goods is not related to "saturation", in the sense the word is used in microeconomic theory: saturation and non-saturation is a static concept. Intertemporally, the capital stock may very well decline, as an optimal choice : we pile up capital early on, and then, the rate of usage is greater than the rate of further accumulation: we use what we have bought in the past, wearing down the stock. 

The right way to model durable goods (and it has been done of course), is to specify a utility function like

$$U = U(C, h(D))$$

where $C$ are non-durable goods and $h(D)$ is the service-flow function related to durables $D$. Sometimes we simply write $C_D$ (consumption of the service flow). The difference is that the stock of durable goods is a state variable, alongside any other state variables the model has.

As a recent example of a theoretical model (not a canonical one), see the paper
Mansoorian, A., &amp; Michelis, L. (2010). Monetary policy in a small open economy with durable goods and differing cash-in-advance constraints. Economics Letters, 107(2), 246-248.

Public Capital also enters sometimes the utility function, to represent the services flow that come from public infrastructure (contrasted to current public expenses). See for example

Chatterjee, S., &amp; Ghosh, S. (2009). Public goods, congestion, and fiscal policy: Do consumption-based instruments matter?