Nothing in philosophy is mere speculation, at least not in the terms that we generally accept it. Speculation in philosophy is as it is because it is ruled by the person making the assumption which is to him a truth defined by his experiences or emotions. To simply say that everything is mere theory is not exactly true because to one person the theory is fact defined by them but to others without the same experiences it is theory. Thus to say that philosophy is mere speculation is the most inacurate judgement of all.
For example take the statement "Never give up without a fight"
This is truth to some people, defined by their own struggles. To others this is theory because they have never experienced a situation where this is true, or had a situation where "Never fight a losing battle" was true. Both however are two sides of the same coin in that they are two different opinions of the same thing. The first says that no matter how hopless always fight, take a chance to win. The other says only fight when you know you can win. Each a fact to the person who believes it and a theory to the other.
Our intellect is limited to creating models or theories to explain observations, but to say that these models are true or not, is beyond intellect. "Truthness" of a theory depends on a "personal trust" on the model. A model or theory cannot prove itself true only by itself, there is always an assumption of ours in there, even if implicit.