Their assumptions are validated by everything else working and showing up as expected
Still, I have a similar feeling, that there may be some hidden 'tuning' to make things match, or some assumptions or values that have been erroneously determined or set.
Many of the parameters are actually not specified by the theory, and have to be fitted by experiment. See http://en.wikipedia.org/wiki/Renormalization for one of the reasons why.
I don't think that renormalization has much to do with this! :P
It's enough to say that the standard model has to have some input from the real world -- mostly the masses of the particles and their mixing angles. Renormalization just makes it harder to talk about what a particle's mass "really" is; it doesn't really increase the number of parameters in the theory.
Renormalisation, however, does suggest that coupling constants[0] change with the energy level involved, which then leads to the nice idea that, given an appropriate theory, one could make all these runnings match at a certain energy and then get a grand unified theory (of the strong and electroweak force) which breaks down at lower energies and leads to our three different coupling constants of the gauge groups[1].
[0] Effectively the basic rate of things happening per particle/energy/volume of spacetime etc., originally assumed to be constant.
[1] Effectively things happening faster for certain types of interactions (electromagnetic vs. weak vs. strong).
Still, I have a similar feeling, that there may be some hidden 'tuning' to make things match, or some assumptions or values that have been erroneously determined or set.