There isn't a 1.5 phone on Sprint and I would be willing to bet the Prime doesn't make it there before January and when it comes out the rumors of the quad core phones will be out. At some point you just got to make a decision and go with it since there will always something bigger, badder, better a couple months down the road.
If the S2 isn't for you then certainly you shouldn't get it, but seems a little crazy for that reason.
It is not about S2. S2 is a bad wild gunslinger who is gonna rule the sprint nation for next few months, and seriously, its hard to beat a samsung phone. Samsung has proven their worth once again this year after a rocking year of GSI. They carve their own silicon with perfection and its hard to beat them. S2 is a good phone and it will remain so. What I was talking about was that hardware and software and their progress goes hand in hand. When hardware improves, software becomes available that can utilize it fully. Desktop era was a good proof of this. Today there is nothing that can use 1.2GHz power of exynos, but soon there will be. Games qualities and graphics are improving fast, and at a time when quad core CPU's will become norm of next year, power hungry apps will come. Sad matter of the fact is that we are still stuck with 2 year upgrade cycle and there seems to be no way out without paying more for the device. So if I or someone else wants to buy a phone for next two years, then its natural to think of what its power would mean against apps that are gonna come 12 months down the road. 1.2GHz is norm of today, 1.5GHz would be norm of 6 months down the road. So 1.5GHz today could help fight off the desire to have the latest at least for next 6-12 months.
Next big phones will keep coming. It doesn't mean the current hardware offering of E4GT is anything to laugh at. I already pre-ordered mine, and I am planning to just keep it in healthy condition for next 12 months, when I will sell it on craigslist and then invest couple of hundred dollar, which is same as upgrade cost with a new contract, and buy big thing at that time. It will be far easier this way than to worry about hardware specs for next 2 years. But I agree with your point that you have to make a decision at some point, and GS2 is perfect phone to help make that decision now.