I've turned on RDM on my Mac and set my resolution to 1280 x 800 and everything looks OK (though not as nice as the 15" res 1140 x 900) and then removed the check box in VM settings and the VM still looks really bad. Not sure why mine seems to be so bad. I'm running WIndows 8 Enterprise.
I don't use Unity either, I like to keep the separate. I already had Clear Type turned on but I've changed a few options and it still doesnt look right.
I know you said you're using a 13", surely it can't be that different for 15"??
I might create a W7 VM and see how that looks, see if it just W8 that doesnt play well with retina. I'll let you know over the weekend.