"If you're going to run Maverick on older hardware like 2009 or lower, you're going to need an ssd hard-drive to get enjoyable experience in my opinion."
I'm sure that an SSD makes ANY hardware more enjobable to use.
But that said, I have a late 2009 Mac Mini and Mavericks runs BETTER and FASTER than it did with its original OS, Snow Leopard. I upgraded straight from Snow Leopard to Mavericks and on Mavericks my Mac runs faster than it did when it was brand new.
I'm not talking boot time--I don't notice any significant difference there--but I dont' reboot that often anyway. Apps are a lot snappier on Mavericks. It's like I got a new computer!
That's my experience anyway.