I keep the '74 Singer Touch N Sew for garments- I'm so used to it, I won't use the Viking Rose to do button holes, I just know it better.
The Rose I use for the fancy stitches. Am going to get over my fear of the embroidery unit and master that this year.
My Juki is my absolute favorite for quilting. It is set up 100% of the time and ready to go whenever I need her.
So yes, it's OK to have multiples. (OK, so I didn't touch on the 3 singers in the boxes to be taken to get serviced- but I'm giving them to DDs and SD- so they don't count.)