Some poor chap spent time creating an optimizer for .mdl models, but it would seem not everyone can be bothered with searching "User Contributions" before making assumptions.
Here might be the MDL Reducer thread which I found in 5.2 seconds on dial-up.
This could be the site for which, you will, no doubt, absolutely, irrefutably, not maybe, might, seemingly, potentially, could have, possibly, apparently, perhaps will, but with iron clad truth behind the statement, make a donation to the developer, if you find the MDL Reducer device useful. Please do not prove the assumption in the previous statement false out of spite or reciprocation; such would not be fair to Hiroyuki.
Maybe, you think the above solution is too easy. Instead you might find some means by which to import the model into Blender and apply a "Decimator" (with a name like "Decimator" maybe you can only expect good things) to optimize the model. I can not guarantee that the results will be satisfactory. In fact, I won't even guarantee that there will be any results at all, I have never "Decimated" a model in Blender. For all I know, the "Decimator" might slice your model into separate triangles and overwrite system files with Blender format files that each contain a single triangle of the source mesh. (Then again, the Decimator might be a figment of my imagination.) Ideally, you might only want to "Decimate" the "flat" faces of interest, but to do so specifically, might require more than I am suggesting.