I bought a pair of MG1's in 1982 or 1983 and sold them to a friend of mine when I upgraded. He still has them, and they sound fine. I'm pretty sure the MG2 is just a bigger version of the same technology--the ribbon tweeters didn't filter that far down the product line until several years later. Based on my experience, you've got a very good shot that they'll sound fine, and, if they do, $300 is a very fair price.
Not sure what you mean by re-furb. If you mean performance-based refurbishment, I don't know how you can evaluate the need until you know what the speakers sound like in their current state. If you mean cosmetic refurb, Maggie used to, and very well still may, sell replacement "socks" for consumer installation, if, for example, someone wanted to change grill colors, or gave up smoking after having kept the speakers in a smoky room. A friend bought the kit for the SMGs, which are much smaller than your pair. I think that it cost a little under $100. He was able to install the new socks without problems, but seemed to find it harder than he expected.
Not sure what you mean by re-furb. If you mean performance-based refurbishment, I don't know how you can evaluate the need until you know what the speakers sound like in their current state. If you mean cosmetic refurb, Maggie used to, and very well still may, sell replacement "socks" for consumer installation, if, for example, someone wanted to change grill colors, or gave up smoking after having kept the speakers in a smoky room. A friend bought the kit for the SMGs, which are much smaller than your pair. I think that it cost a little under $100. He was able to install the new socks without problems, but seemed to find it harder than he expected.