Tradition plays a difficult role in liberalism - one definition of liberalism is the trend in a given society that seeks to reinvent it, breaking traditions to make its reinvention based on new norms possible. This is a continual process - the liberalism of one society or one time period may not be continuous with that of another. This is not central to our definition - I hope to describe the values and ends of a particular liberalism - that of western society, constrained to be compatible with but not restrained to imply socialism. Our consideration of tradition is not intended to accept or hold as intrinsically good existing traditions. It is designed to understand humanity by understanding the needs and concerns to which tradition adapted, to gather ideas from them, and as examples of working systems. Our liberalism values other traditions as things to learn from in construction of our views of the future, not as intrinsic values. We further recognise no propriety in the traditions of others, neither giving special attention to "pre-liberal" versions of the societies from which we come beyond shared values nor "keeping our hands off" of traditions of others designed to respectfully preserve their distinctiveness.
Acts of tradition are not valueless - they are also not intrinsically valuable. They share some common purposes - to define a culture and aid its social solidarity and to help pull attention of a society away from functionalism. The content of many traditions shapes people beyond this - just as metaphors from the Qur'an in Arabic shape everyday discourse, repeated traditions suggest certain traits, ways to deal with problems, and concerns of a culture - the celebration of survival against frequent oppression present in many Jewish holidays define part of the Jewish cultural identity.
Traditions of existing societies are valuable in that they provide examples of working societies. As we work towards implementing our ideas, we cannot directly use traditions of others without consideration - traditions fit together to shape those who hold them and make them to some extent suitable for the system in which they exist. Understanding such processes and seeing how they fit together gives us valuable information on both the process of social engineering and tell us what might stand the test of time. The Haggadah, for example, helps to define those parts of modern Jewish society that use it to organise Pesach, and has done so in various forms for almost two millenia. Likewise, Ashura helps define (particularly Shi'a) Islamic society. The values of a body of people are useful in that they inform us about one permutation of culture that is possible and thus help us understand the line between what kinds of society are viable and what are not. For any movement that would reshape society (regardless of particular direction), this is critical to avoid disaster.
It is a liberal perspective to learn from existing traditions, treating them as useful information on social engineering but their contents as not intrinsically valuable outside of that.