How severe and how old are the lates?
As lates age, the less they hurt.
GW letters only cost you about 50 cents, so I say send them every so often and you might eventually get someone who will listen.
You might use the card a little bit and PIF for a few months before you start sending them again.
1 late in JUL 2005 which went into another late in AUG 2005. They weren't ever worse then 60 days late and I've never had a problem with them before. I guess they weren't hurt as bad if time goes by but I'm planning on trying to purchase a home within the next year or so.
If you go FHA, they only pay attention to lates in last 2 years.
I say use the card some and then try GW'ing again.
You don't have much to lose by sending GW, but a lot to gain.