ACDC Premium is one of Stern's best and arguably one of the finest pinball machines ever made. Having said that, I have owned the Pro for over 3 years with no intention of selling. Let's break down the differences:
Swinging bell: sorely missed on the Pro, but Hemi's bell mod or the new LED version is a decent alternative
Color changing inserts: nicely integrated, but not as dramatic as other games (Met, ST, etc.)
Train: just a toy that can be purchased separately; I have one on my Pro
Drop targets: probably the biggest difference between the two models beside the lower playfield; a straight shot to the TNT targets is sudden death; this is personal preference and likely linked to the 'speed' everyone mentions when discussing the Pro... it makes the game play very differently and changes shot strategy; speeking of speed, how many Premium owners disable the crossover ramp?
Finally, let's discuss the lower playfield. It's a love it or hate it feature so I won't offer opinion here as someone will contradict it. I will mention this: How many Premium owners, after a few years of ownership, jump up and down for joy when they're in the lower playfield?
To sum up, the differences are worth it to you or not, but understand they are two completely different games. Folks will say the Pro is stripped down, and I would agree to a certain degree. You'll likely want to mod your game... LEDs, train, FF speakers, Helen decal, bell mod, powdercoat, etc. But once it's ready to go, prepare to have your ass handed to you unlike any other Stern game.