Let me tell you what’s worked for me:
Keep writing letters. Encourage like minded people to keep writing letters. You may be doing more good than you think, though it might not be apparent.
Become part of the solution. If you don’t know much about the faith, learn it. After you learn it, get involved in teaching RCIA or other Adult Ed. If you become more of a known quantity in the parish, you will be in a place to have your views heard. You will also have a change to teach others orthodox teaching.
Always be respectful and reasonable. If you want to hurt your efforts to bring more orthodoxy to your parish, be a rude crank who looses his cool, and resorts to namecalling and public griping.
Be patient. Things change slowly, but it God’s behind it it will bear fruit.