Started with cardboard standups, but haven't needed them in years. I have about 40 minis, and I'll proxy as needed. I'm willing to use the cardboard from my 4th ed box, but I would use one or the other - not mix them during a game. If I got into the game today, I'd like use whatever came in the box, and not pay for anything else. I'm not a mini collector - I just happened to acquire some on the cheap. As for terrain, I think it looks great in a static diorama, but isn't worth the effort to play on it. A large number of paper hex maps is far better than one static piece of terrain that is used over and over.
A problem I see is that even if cheap plastic minis are included in a box set, too often they get painted up nicely, and then need special carrying cases so they don't get damaged in transport. With the cardboard, having everything in one box, and not caring so much if they get beat up, I see as a distinct advantage.
At times, I wish the boxed sets included a set of cardboard standups, and then maybe a lance of plastic to get people interested in something better. And have free or very cheap downloads so that people could print out new cardboard when they needed them. My preference is that the cardboard is closer to map scale than mini scale, but that's just me.