I've owned, carried, and used variations of both knives. I've had the Sage 1 & 2 (still have and carry the 1), and several variations of mini-Grips including Ritters. Don't have any left now. The biggest mini-G drawback for me was their short length. A 3-finger grip in a hand that has 4 working fingers and a thumb doesn't do it for me. A lot of my cutting involves fairly tough industrial packing/strapping materials where I need to put a bit of pressure into the cut, even with a sharp blade. I want to be able to hold the handle with all 4 fingers. I can do that with the Sage, I couldn't wth the mini-G.
The blade steel isn't that big of a differenece and you can get a mini-G with S30V or D2 if you want. Also, there's nothing wrong with a well-designed liner lock and spyderco designs theirs as well as anybody. 'Course, there's nothing wrong with an AXIS lock either; absolutely ambidextrous and easy to operate, although I think it's more comfortable to opeate on a somewhat longer handle like the 525 or 1530 Bone Collectors have. The mini-G didn't feel cheap to me because I actually like FRN (Noryl, or whatever BMcalls it). The biggest reason I kept the Sage 1 and fired the mini-Gs was just that they were too small for my average sized hands (I wear a L men's work glove but they're just a bit loose on me). If you decide on the mini-G, I'd suggest looking at the mini-Ritter version. I do really like that blade shape and the slightly wider blade that they have.