I did that back in the day. It was between LBT 7 and 8, I sent them like a dozen letters over a period of about a year. Since the franchise wasn't dead back then, it was mostly "thank you for making these movies", suggestions for future movie plots, fanart of the characters, basic kid stuff. They completely ignored me.
Then I wrote a single letter to GI Joe with similar sentiments, and they sent back a thank you letter with coupon for 10% at Toys R Us. So yeah. Save your energy and send the letter to a studio who actually cares.