Frankly, the biggest difference I immediately see is the difference in batteries:
Whereas the FT-60 uses NiMH batteries, the FT-70 is lithium-based.
There's significantly higher energy density in LiIon, which explains the weight difference, and: a charged LiIon battery will hold load without noticeable charge loss for weeks to month (depending on design, even years, but that won't be the case here), even after intense use¹, while NiMH does suffer under high self-discharge right from the start.
Other than that: the generation change implies better DSP, leading to probably better speech understandability, lower power usage.
The firmware on the FT-70 is updatable; this might or might not turn out to be an advantage in the future.
¹ battery design is an involved topic; of course, there's limiting factors here: discharging at high rates under very cold conditions might lead to increased self-discharge etc, but it's pretty unlikely your LiIon battery will ever see the same self-discharge rates as brand new NiMH (wikipedia says 0.5% to 4% per day
for NiMH at room temperature, and medium-sized lithium polymer batteries typically do something like 4% in a month