In my opinion, it isn't worth installing. I installed it on my spare Macbook White (8GB, SSD) and it doesn't show anything interesting for old Macs. Window management is also a bit buggy with the merging of maximize+fullscreen functions. The user-interface looks a bit lame (GUI elements are bigger and unecessarily flat or non-polished). Yosemite is a major redesign on GUI elements (although usability remains the same) and a minor redesign on internals (except the signed kext drivers, whose measure prevents malwares, but also custom drivers, like TRIM-enabler or custom CUDA packages for old GPUs).