IMHO it's huge. You also would have the same guide on both with a mini, so when you scroll through looking for things to record it won't matter which tv you are at, you'll see if it's set to record. You have to actually remember what you did if you stick with non minis.
The only reason is if the genie goes down you don't have tv for the day or two it takes to get it swapped. And that's assuming you don't have over the air. IMHO, that's the day you watch a blu Ray if it ever does happen.
I'm actually not that concerned with the system going down unless it's on a Saturday or Sunday during football season when I really rely on DirecTV. I have cable as well and the only reason I keep DirecTV is for Sunday Ticket. It certainly gets expensive having both but I just can't get rid of DirecTV. I suppose I could suspend my service from February-August but I'm not even sure if they allow that. Plus I'm sure I'll have to keep my service active once they upgrade me to the Genie.