I read extensively about the Storm and I have seen no hints at a 2nd Gen model. I think the 2nd Gen iPhone took over 2 years to emerge. Right now I would only expect upgrades in the OS.
Unless you are planning to wait for another 2 years, I would go ahead and get the phone. But be aware, unless you have the temerity to fiddle with boot-leg beta OS's, the current OS .75 still has its issues. If you are thrilled with your current phone, I might be inclined to wait for the next OS upgrade to see if all the major kinks are worked out.
I love my Storm and it does everything I want (SMS, MMS, calls, email). It really depends on how thrilled you are with your current phone.