afaik, solenoids have rated duty cycles and max. on times to avoid overheating and other problems (some can be always on). I had assumed that the valve types, as you mention (and like the one I recently replaced in my dish washer) are designed for the duty cycles and on-times they receive.. However, a qbert (pinball) knocker is activated for very, very brief moments, and not very often. Such a device is not necessarily designed to remain on very long. Also, as I understand things, a solenoid will offer very little resistance after the inductance settles, and so controlling current (amps) can be an issue.
Here's an example of several duty rated solenoids:
http://media.digikey.com/pdf/Data Sheets/Pontiac Coil Inc PDFs/M-22.pdfNote in the linked spec sheet the Pulse rated one says On for 100ms, Off for 900ms. I'm assuming you'll run into problems if you push it a lot harder than that - even with proper voltage, etc. It's just a property of its construction.
Of course, a fuse, whether redundant or not, is always good. I've blown several, so it's been good having it there to protect other components. I'm blowing it partly because I don't have specs for the solenoid, and mostly because don't know what the hell I'm doing
Afaik, this thing is used in pinball tables at higher voltages than I'm feeding it, so maybe it's just meant to eat more current than I'm allowing for or...? Anyway, it's been running fine for a while, thanks to many people who've contributed to this thread, MonMotha, MameHooker, etc.
also - the diode on the solenoid is a must, regardless - I think we're all agreeing on that.