ajlaird mentioned Virtual Pinball, I think that Visual Pinball can be really valuable with regard to rules and especially Sounds/Music.  There has been games that I just wouldn't be able to have in a small collection because the music would drive me nuts, of course in a giant collection it wouldn't matter so much. This program alone, got me back into playing pinball and into buying real machines, and it's what I used to figure out what I liked and didn't like of the DMD era that I missed out on playing in the wild.