An acceptable answer (for my purposes) would either
a. show that there are other items used for a Mitzvah, other than items with specific holiness, such as Tefillin, Sifrei Torah, etc., which we kiss while performing the Mitzvah or while preparing to perform it, and that this sort of thing is very common across various types of Divrei Mitzvah
b. show that this is unique to Tzitzith but that there are good reasons for kissing them at specific times (as in those other answers).
While I'm slightly inclined to think that b. is the answer, as I cannot think of other Divrei Mitzvah that we kiss, there is a nagging feeling that there is something either about doing a Mitzvah (and then we have to explore why we don't kiss other Divrei Mitzvah) or something special about Tzitzith that can be pinpointed, because not only do we kiss them at various parts of Tefillah (and Tzitzith are not only for Tefillah), but we kiss them when we don them (ie., we kiss them when we perform the Mitzvah).
(Speculation: Could it be that kissing them is either part of the Mitzvah or a Hiddur Mitzvah, akin to shaking a Lulav or wrapping Tefillin around the fingers?)