If you think you can get good scores on the subject tests, there would be no harm to taking and submitting them to colleges. Also, your ACT score isn't fantastic, especially if you'll be applying into engineering (which it seems like you will). Those schools engineering programs are competitive to get into, so you want to get every advantage you can.
If you take subject tests, you should definitely take math and then pick the science you are best in (same engineering assumption). If you are confident in the humanities, you can take one of those tests as well.