Taking a look at Spike (1) from a technical stand point: The system uses some really good and modern concepts; let me go into some details.
It is using an isolated serial bus for communication. This basically confines faults to the faulty nodes. Even high-voltage-to-switch failures will only fry the switch node, but leave the CPU ok.
A single high power medium voltage for all mechs and all nodes allows a simpler/more efficient power supply. Having a proper high power DC system eliminates common fliptronic problems like bad rectifiers, fluctuating supply voltages and most of the stuff that often make WPCs sluggish under certain circumstances and are a bitch to figure out and fix.
5V for all lighting simplifies node/driver design immensely.
Distributing the computation effort throughout the machine (and having at least a little processing power on the nodes) allows for all the neat things we've come to like, like RGB leds, instant kickbacks, more controlled mechs...
Endless processing power. Even Spike 1 has a 400MHz CPU with 64MB of ram. For something a computationally simple as a pinball game this is plain joyful overkill
But there are downsides too.
SMD can be tough to repair if you're not used to it. I personally like it more than through hole (especially with old boards that tend to loose their traces), but most people will probably have a hard time with SMD. But they are definitely repairable, saying that you only have the option to buy new boards is bogus.
Parts can be harder to obtain. From what I've seen Stern uses stock common parts, but you don't likely get them at your radio shack. Iirc the bus is powered by some automotive transceiver chips, so even that should not be a problem. However we do not know how supply will be in 15 years when there is a new generation.
And the imho most important argument is that Stern uses programmable controllers with embedded flash memories on all the node boards and the cpu. You can not just replace those with a new blank part. While the controllers are not hard to acquire, the software is. Unless Stern releases binaries for the node boards or they can be extracted from either existing boards (which can usually be prevented) or the spike update files, we are pretty much screwed. The node board NXP MCUs do come with a basic bootloader, however I would not count on spike just accepting and reprogramming a blank one. If it does, then this is point is invalid .
The CPU itself does have an embedded ROM that does boot the system from the SD card, so that should be fine. However the CPU is a BGA chip, swapping that is something that required special equipment to do.
On the Spike 1 CPU board there is a second AVR controller (with embedded flash); I guess that is taking care of the RTC and maybe the DMD. This would be prone to the flash problem too. And since flash usually just has a guaranteed data retention time of 10-20 years this might really become a problem somewhere down the road..