I think it needs to be pointed out that in ~2007/2008 the market crashed, and with it the value of most collectibles. Comics included. It's not surprising that individuals have seen fairly fantastic gains over the past 10 years. The rebound, along with the introduction of DC and Marvel cinematic universes, have kicked things into high gear.
Many issues, such as Hulk 1 and TOS 39, have likely already seen the majority of their growth. In fact, you could argue that they'll now likely start to dip a bit as The Hulk and Ironman fall out of the public eye a bit. Whatever you do, don't put all of your eggs in one basket, especially if you're planning on buying at a high point.