People tend to mix these concepts up a lot despite that they don't neccessitate eachother. A decision or statement can be theoretical yet be based on certainties (the field of mathematics is an example) and a statement can be speculative yet concern only real scenarios that have occurred before and/or aren't in any way dubious as to the real possibility of coming about.
So what does the difference consist in?
I think a pretty obvious possibility would be:
Is it this simple? Can we confirm, for example, that Ne types dislike speculation despite that they like theory?
I think I can confirm this last thing as far as I myself am concerned. As a Civ IV player I always hate it when people advise me to "settle in place, I've got a hunch that grassland tile has a hidden copper resource on it". Speculative typings in socionics tend to annoy me, too ("person X has oval eyes, I think she may be INFp"). And it's not a secret that Gamma NTs feel a lot more at home in bussiness than Alpha NTs do. I tried to study up on stock dynamics a while ago but decided that finding one's way among all the randomness was a pointless task, at least for someone of my dispositions.
How do we further clarify and describe the difference between the two?
A theoretical statement is an asserted possiblity as to how something might work apart from being proven to work that way. A speculative statement is an asserted possiblitiy as to what might be the case.
Notice I use "theoretical" in the collquial sense here. In science, "theory" implies proof, but this usage is very uncommon in ordinary speech.