It is trivially easy to hack a network that is controlled solely with MAC security. It is a useful hygiene factor to stop casual war-drivers, but it is hackable in a remarkably short amount of time. In fact the IEEE has a task group looking at encrypting management and broadcast frames (802.11w). It is through unencrypted management and broadcast frames that most attack vectors into 802.11 come.

Even if you decide to trust MAC security, if you only have a single wifi access point you are stuck with having to add the MAC address of every new device that you use on the network - so you are adding new devices every time a friend wants to use their laptop or android device. Not all of us can have the luxury of multiple access points - living in the middle of Manhattan, it is hard enough to get a single access point running with minimal interference there are so many wireless networks in a detectable radius.

Regarding spare parts. Philips might be required by european law to provide spares for discontinued products for many years to come. They are not required to provide them cheaply. Have a look for spare screens from mobile phones that got discontinued 5 years ago. The prices can range from very little to exceptionally high depending on whether spares were stockpiled. Or even try and buy an identical replacement remote control for a device that you bought 5 years ago. The reason I ended up with a Pronto in the first place (an RU890 for the Pronto geeks) was because I smashed a couple of remote controls during a move and when I researched the cost of replacing the remotes it was significantly more expensive than getting a Pronto.

Buying in to obsolete products can be a minefield, especially in the fast moving space of IT. I doubt I'll replace my pronto within the next year. But unless Philips manage to sell the pronto line to another company and it continues, I doubt I'll be using any pronto products in 5 years.