I don’t think that’s quite correct: property for Locke clearly has value prior to our “ownership” or acquisition claim insofar as the proviso “still enough and as good left” (indeed, ‘So that in effect there was never the less left for others’!) refers to the fact that property has some sort of value prior to our appropriation (for example, we enjoy, however insecurely, possessions in the state of nature prior to the private property of society), property is a peculiar enough kind of worldly resource to prompt Locke to qualify his story with the aforementioned proviso. Labor has significance owing to its addition of “use-value” (and not, as with Marx, ‘exchange-value’) while property itself has “intrinsic value” owing to its “usefulness for the life of man” (natural resources, in addition to having intrinsic value, may, from Locke’s vantage point, have some small or insignificant amount of use-value prior to the addition of labor: fruit may fall from trees sans our labor, i.e., ‘land frequently produces consumables without any labour having been applied to it’). This has been well-explained by the late G.A. (‘Jerry’) Cohen,* who notes many (even Locke himself on occasion) are prone to confusing or conflating the “value argument” with “the argument from labour mixture: “ “If the justification of your ownership of what you have laboured on is that your labour is in it, then you do not own it because you have enhanced its value, even if what deserves to be called ‘labour’ necessarily creates value.” The “investment with value” centers on the conferring of value, not the labor by which it is conferred. Locke later does bring the enhancement of value into the picture (and notice, this is not the same as ‘creation’ of value but the enhancement of existing value), but that is after the initial appropriation of property, the right to which is initially held in common. As Cohen explains, “in the logic of the labour-mixture argument, it is labour itself, and not value-creation, which justifies the claim to private property” (See Ch. V of his Second Treatise of Government). Locke later brings value-enhancement into the picture in an attempt “to justify the extensive inequality of goods that obtains now, when original appropriation has long ceased. The justification Locke offers is that almost all of present inequality is due not to any unequal initial appropriating but to the labour which followed after initial appropriation.”
It is interesting that both Locke and Fichte subscribed to the “self-ownership” thesis. For Locke, “every man has property in his own person,” and Fichte states that “Man can neither be inherited, sold, nor be made the object of a gift; he can be no one else’s property because he is his own property.” On this, of course, Fichte differs with Kant, the latter finding the notion of self-ownership to be incoherent (and while not subscribing to the normativity of the self-ownership thesis, G.A. Cohen argues the concept, pace Kant, is in fact coherent).
And for the specific weaknesses in Locke’s argument with regard to labor and use-value, see Chapter 7 of Cohen (below), “Marx and Locke on land and labour:” “If there exists a defensible criterion for assigning relative contributions to output of labour on the one hand and the original properties of the soil on the other, then it is not Locke’s.”
* See his Self-Ownership, Freedom, and Equality (Cambridge University Press, 1995).