I'm curious as to what it is about the school model machine you bought that is causing you problems. Perhaps all it needs is a tune up.
I would stay away from buying a machine at JoAnn's if it anything like the JoAnn's in my area. The employees there don't know as much about machines as I do so support would be nonexistent. My daughter-in-law had terrible luck with a newer Singer she bought at JoAnn's so I would also stay away from that brand based on her and others experience.
Go to several dealers and test drive machines. Go especially to the Janome dealer and talk to them about your current machine. I have a Janome and it is not clunky and sews like a dream. Check out the used models at the dealer as well. There can be some really good buys there.
I understand the emotional attachment to a machine. I recently let a 1950's Kenmore go that was my mother's and then mine. It had finally sewn its last. I'm still questioning whether I could have patched it together again and still have it.