It's a bit difficult to say because it all depends on what type of sound you're going for. Your friend might be right in saying you should get the line 6 board. It does provide a lot of variety in amp sounds and effects. That being said it's probably not going to turn your Princeton into something it's not. It'll def help out if the tones are bad from the amp but at the end of the day a bad sounding amp is going to sound bad no matter what. I suppose if it's a case of you liking the clean sound of your amp and you can sculpt the overdriven tones w the line 6 it'd work. You could take your amp to guitar center and try out the line 6 w your own gear and see if it's to your liking. I'm sure they'd be happy to help you out.