It is not possible to upgrade to R-link. There is a thread on here discussing some of the details, but in essence the R-link system has connections into the car's systems that medianav does not. So the wiring loom to the medianav system is different to R-link.
The only way to get R-link is to order a car with it in.
I would say the updates via the toolbox are essential. It will give you the latest, available, maps. That process is a two-step activity if you have not updated before on your new car.
The toolbox will not give you any more facilities on your MediaNav, however.
There is an update that gives you full postcode destination selection, but you have to pay £57 for it. I am quite happy selecting an address from the drop-down list that the default partial postcode destination selection gives.
Edited by: crossbow