The newer snapdragon has the following benefits:
Much better GPU. The older snapdragon (on the Inc, EVO, etc) ha an inferior GPU. One of the reasons it stayed viable is that all the other processors on the market (ignoring for now tegra--we are looking at ones in phones in the past year) were ARM cortex-A8 chips. The Hummingbird and OMAP are just slightly modified A8's, and thus they performed better than a stock A8. HTC said that they would use the ARMv7 instruction set (the same one all the other processors use), but that they would build their own processing core and call it Scorpion. The Scorpion core is much more optimized than the slightly modified A8 cores, and thus even with the vastly inferior GPU, the first gen snapdragons were real competitors in the SOC market.
Now, with a fairly good GPU, the second gen should fly. And, if the MT4G is any example, it does.
The second gen is also a 45nm process as possed to the 65nm of the first gen. This leads to more transistors per area of space = more processing power. Also, with the decreased printing length comes lower resistance, so each transistor takes less energy to use (this is a simplification--PM me for more scientific explanations).
-Nkk